Supercapacitor is a new kind of storage device between conventional capacitor and battery, which was extensively studied due to their promising properties in terms of high power density, reversibly charged/discharged at higher rates, long cycle-life, wide working temperature, and environment-friendly have been applied widely in many fields that electric vehicle, uninterrupted power supply, aerospace, military affairs. Recently, supercapacitor is given more and more attention to the public, it has become one of the attractive research fields. Currently, the commercial supercapacitor electrode materials are focus on carbon materials, but they exist many prombles, such as low capacitance, non-uniform pore size distribution to be resolved. Tremendous efforts have been devoted to developing active electrode materials for supercapactance applications, searching new carbon resources, activation technology, controlling means of effective pore structure and surface activity, research and development of carbon composite materials, reduce production costs to improve the electrochemical performance. The acivated carbon is highly important and widely used in supercapacitor in its larger surface area, better chemical stability. Although there are many reports that using the cotton stalk to prepare high surface area of activated carbon material, the cost-effective porous carbons derived from cotton stalk is investigated as the active electrode material in supercapacitor for the first time. In this thesis, the porous carbon with high specific surface, carbon composite materials were prepared from the biomass resources of cotton stalk, by the process of different activation methods. The surface morphology of cotton stalk based porous carbon and structure characterization were analyzed by means of thermogravimetric analysis, nitrogen adsorption-desorption test, SEM, XRD. The influences of the activating temperature, activating time, the concentration of H3PO4, the ratio of H3PO4 to cotton stalk (solid-to-liquid ratio), specific surface area, pore structure and morphology of porous carbons derived from cotton stalk had been investigated. It was prepared as electrode material, all the measurements were carried in 1.0 mol?L-1 Et4NBF4/AN electrolyte. The effects of different activating parameters on galvanostatic charge-discharge performance, cyclic voltammetry and EIS of porous carbons electrode material. The optimal technologic conditions of preparing porous carbons based cotton stalk were established. (1)The cotton stalk from Xinjiang Province as raw material due to wide material source, low price, high fixed carbon content and low ash content. The whole pyrolysis process could be divided into three stages. The ?rst stage occurs between ambient temperature and 600 ?C and a minor weight loss observed is mainly due to H2O release by evaporation and the sample decomposed to uncondensable gas (CO, CO2, CH4, H2). The second stage is in the temperature range of 600-800 ?C and the strongest weight loss observed is attributed to the thermal decomposition of the raw material, these reactions are accompanied by further chemical transformations that include dehydration, degradation and condensation with a loss of aliphatic character and a corresponding increase in aromaticity and simultaneous release of gases. The third stage appears over a wide temperature range from 800 ?C to the ?nal temperature and a slight weight loss. It is indicated that the active sites on the carbons had reacted completely, and H3PO4 on the botanical structure through the penetration and dissolving of some components by breaking chemical bonds and it is followed by recombination to form a more thermally stable new polymeric and aromatic structures. So the activation temperature of 800 °C is more perfect than others for preparation of porous carbon from cotton stalk. Preparation of porous carbon from cotton stalk by H3PO4 activation method. The structure and performance of porous carbon are influenced mainly by the activating temperature, when the cotton stalk particles is 200 item, the mass ratio between cotton stalk and phosphoric acid solution(50%) for 1:4, activation time is 2 h and activation temperature at 800 °C, the porpous carbon have larger specific area(1481 cm2 g-1), microporous volume for 0.0377 cm3 g-1, and the average pore size of 2 nm. It has excellent electrochemical performance, The specific capacitance can be reached 114 F g-1, and without capacity fading after 500 cycles. (2)Manganese oxide/porous carbon composites were synthesized by H3PO4 activation. the improvements of porpous carbon modified by MnO2 were confirmed by the experiments of galvanostatic current charge/discharge, cyclic voltammograms(CV), alternating current impedance tests, respectively. The effect of different concentration of MnO2 on the electrochemical properties was investigated. It is indicated that different proportions of MnO2 did not affect the structure of the porpous carbon composite, and micrograph of the cotton stalk porpous carbon modified by MnO2 preparation conditions.When the mass ratio of MnO2 is 5%, the specific capacitance of composites electrode at 2 A g?1 is 160 F g?1, The composite capacity increased 39% than before. On the other hand, the specific capacitance without capacity fading after 500 cycles, the CV curve has rectangular shape between positive and negative at 50 mV s?1, and the prepared carbons show lower diffusion resistance in 1.0 mol L-1 Et4NBF4/AN electrolyte, the internal resistances was estimated to be 20 Ω for the carbon composites for 5% MnO2, It has excellent electrochemical characteristic. (3)Studying on preparation of porous carbon based cotton stalk electrode material by KOH- activation of gradient constant. In order to improve porpous carbon from cotton stalk electrode material specific capacity, preparation of porpous carbon based cotton stalk as electrode material by KOH-activation of gradient constant temperature for the first time in our laboratory. Firstly, the cotton stalk powder was carbonized at 800 °C, the carbon sample was impregnated with KOH solution (5 mol L?1) with a mass ration of 1:4, at activation temperature of 600 °C, 700 °C, 800 °C for 1 h, 1 h and 2 h, respectively. Significantly improved that the specific surface area and pore structure than the direct activation method in the experiment. The surface area of 1877 m2 g?1, total pore volume of 1.337 cm3 g?1, and especially the larger percentage of micropore (404 m2 g?1), It exhibits excellent electrochemical properties and the highest specific capacitances of 180 F g?1 in 1 mol L?1 in Et4NBF4/AN electrolyte at 1.0 A g?1and also displays high-rate long-cycle electrochemical performance even at a current density of 2 A g-1, the high specific capacitance of 180 F g?1. only 1.5% decrease of the specific capacitance is observed after 500 cycles at a discharge density of 2 A g?1. These results demonstrate that the porpous carbons derived from cotton stalk exhibit well cycle stability and very high degree of reversibility during repetitive charge-discharge cycles in organic electrolyte.