The fatty acid mixed was prepared by hydrolysis from waste vegetable oil in subcritical water in order to study the conditions and its kinetics. The results showed that the optimal hydrolysis conditions of waste vegetable oil in subcritical water were obtained as follows: reaction temperature 280 ℃, volume ratio of waste vegetable oil to water 1∶3.5 and reaction time 30 min. Under these conditions, the conversion rate of the waste vegetable oil reached 98.1%. The kinetics analysis results indicated that the average reaction order n＝1.123 89, the activation energy Ea=70.87 kJ/mol, frequency factor A=1.7706×105 and the reaction kinetics model were -dcA/dt=1.770 6×105e-70.87/RTcA1.123 89,respectively.