By Perkin method to synthesize cinnamic acid，the influence of molar ratio of reactants，the type and dosage of the catalysts，the type and dosage of inhibitors，reaction temperature and reaction time on the yield of cinnamic acid is studied. Experiment results show that the optimal condition for cinnamic acid synthesis is the ratio of benzaldehyde to acetic anhydride 1：3，4.5g dosage of anhydrous potassium carbonate as the catalyst，2% hydroquinone as the inhibitor，2h reaction time，170 ℃ reaction temperature，and the yield of cinnamic acid can reach 69.32 percent. This technology，with simple process，easy operation，no environment pollution and high product purity，is relatively an ideal method to synthesize cinnamic acid.