A reaction kinetic model is proposed for immobilized S. aureofacien's protoplasts which can facilitate the conversion of lincomycin into clindamycin. The simulation result of the model has been given. Effects of various kinetic parameters of the reaction on the conversion rate are given in the formula. The formulas which can be used to calculate the maximum conversion rate and the optimal reaction time have been given. The results of model simulation are in good agreement with the experimental results.