Abstract: On the basis of the study of semi-batch esterification of higher fatty acid by methanol in agitated reactor, the authors proposed a three pools mixing model taking into consideration the effects of temperature, pressure, catalyst, reactor volume and condenser hold-up. The present model is solved by using a Runge-Kutta method with varying steps. It is shown that the agreement between calculated values and experimental data is satisfactory. The model is applicable in simulating the semi-batch esterification of mixed higher fatty acid in the temperature range between 378K and 513K with or without catalyst and under the pressure up to 2 MPa.