The isomerization principle of methyl ester of cottonseed oil was studied by UV spectium analysis. It was found that odine was superior to dicyclopentadienyl iron when used as catalyst for isomerization. The optimum conditions of the reaction were that catalyst dosage was about 0.3% of the mass of methyl ester of cottonseed oil, reaction temperature was 180℃, and reaction time was 5 h, the reaction should be acted under protection of nitrogen. Under the optimum con-ditions, the conversion of nonconjugated linoleic acid is 56.1%. higher than that of reported paper.