Diallyl phthalate, whose structure was identified by IR and 1H-NMR, was obtained by allyl alcohol and phthalic anhydride. A series of influential factors to the reaction, such as the mole ratio of allyl alcohol to phthalic anhydride, amount of tosic acid, different kinds and amount of inhibitors and volume of methylbenzene were investigated. The appropriate reaction condition are as follows(based on 0.1 mol phthalic anhydride), n(allyl alcohol):n(phthalic anhydride)= 2.4:1, amount of tosic acid 0.8 g and 4-hydroxyl-2,2,6,6-tetramethyl piperidinyloxy nitroxide radical 0.32 g, volume of methylbenzene 35 mL, ,reacted under reflux condition until no water generated, the yield of diallyl phthalate is about 96.5%.