To study the effect of tricresylphosphate(TCP) additive on the hydrolytic stability and the process of the hydrolysis of ester oil of pentaerythritolester(PE),the method of ASTM D2619-09(Beverage Bottle Method) was used to accelerate the hydrolysis of PE containing TCP at different mass fraction,the relationship between the hydrolytic stability and time was summarized by measuring the acid number of the oil layer,acidity of water layer and the change of the copper strip.The products of the hydrolysis was analyzed by FTIR to discuss the process of the hydrolysis.The results indicate that the acid number of PE tends to increase with hydrolysis time as the exponential type,acidity of water layer is increased linearly with time and the copper strip is corroded gradually,and the three indexes are increased much faster with more TCP.The FTIR shows that TCP is hydrolyzed to phosphoric acid,and the increase of H+ catalyzes the PE to hydrolyze fastly.