Equilibrium equations of a binary mixture for molecular distillation were derived on the basis of heat and mass transfer in liquid films. Simulation on separation of tocopherol from rapeseed oil deodorizer distillate was carried out. Evaporator temperature of model was 20K higher than experimental value, and relative error of tocopherol concentration was below 15% when high tocopherol concentration was obtained. Results showed that tocopherol concentration increases with the enhancement of evaporator, while feed temperature decreases with feed rate. It provided theoretical basis for the separation of tocopherol from deodorizer distillate.