The Effects of operation mode，catalyst composition and loading, amount of solvent, reaction pressure and temperature as well as water addition on the liquid phase catalytic oxidation of beta -methylnaphthalene to beta -naphthoic acid over Co-Mn-Br catalyst have been investigated in a high-pressure reactor. The results showed that the pressure-constant operation mode was better than the stepwise pressure rise operation mode. It has been demonstrated that oxidation occurred with an induction period, and the time length was determined by both the catalyst composition and oxidation conditions. More Co or Br in the catalyst speeded up the oxidation, while more Br resulted in the formation of deep colored products. Water had a negative effect on the oxidation, and the reaction did not happen with 7% water addition. Using a Co-Mn-Br catalyst of 1∶1∶2 atomic ratio with the pressure-constant operation mode, the appropriate reaction parameters were: 1% catalyst loading, 120 ℃ and 0.6 MPa. Under these conditions, a beta -naphthoic acid yield of about 93.7% was realized.