A laboratory pilot unit has been developed to solve the issues of thermodynamic equilibrium shift for the transesterification of vegetable oil into biodiesel. It consists in a two stages continuous heterogeneous catalytic reactor operating at 50 bar and 175 degrees C. Under the working conditions, only one homogeneous phase can be assumed. The reactions of transesterification need a large excess of methanol implying an additional energy consumption and higher capital expenditure because of larger size of equipments, and operating pressure. In this work, a numerical model has been developed in order to better understand the different coupled phenomena (thermodynamic equilibrium, kinetics, mass transfer limitations, etc.) governing biodiesel production. The model is based on a heterogeneous plug flow reactor with axial dispersion taking into account mass transfer in the catalyst and dynamic aspects. The reactor is supposed isothermal since transesterification reactions are almost athermic. Kinetic parameters have been optimized by comparison with experimental results previously obtained by IFPEn. Simulation results are used to establish the future experimental conditions that will be used on the pilot unit. Mass transfer limitations are characterized by changing the diameter of catalyst particle. Concentration and reaction rate profiles are depicted in the fluid phase and in the catalyst. The simulations indicate that a conversion of triolein of 87% can be reached with a methanol to triolein molar ratio of 36 at reactor inlet and with a mean residence time of 1 h.