Abstract: A kinetcs model of immobilized cellulase was developed with inner diffusion limitation and product competition inhibition considered. Then the effects of Thiele modulus, product competition inhibition, and substrate concentration on the substrate distribution in the enzyme particle were investigated based on the model, and effectiveness factors were also obtained. Results showed that Thiele modulus reduced the substrate concentration in the particle and decreased the effectiveness factor; the product inhibition increased the substrate concentration in the particle, however, its effects on effectiveness factor were shown to have dependency on Thiele modulus and substrate concentration; Thiele modulus and product competition inhibition were found to inhibit each other; the substrate concentration increased the concentration in the particle and the effectiveness factor, additionally, reduced the effects of Thiele modulus and product competition inhibition.