An improved model for enzymatic hydrolysis of cellulose is developed that considers oligomer reactions with beta-glucanases, inhibition of oligomers to cellulases and enzyme decay processes during hydrolysis. Our oligomer reactions with beta-glucanases are modeled based on the enzymatic glucan chain fragmentation kinetics to describe the further fragmentation of oligomers in solution after being solubilized from the insoluble glucan chains. The inhibition effects on all cellulases by different types of cello-oligomers are then taken into account by competitive adsorption of cello-oligomers to the active site of cellulases, which is a critical factor contributing to the decrease in the rate of enzymatic hydrolysis of cellulose. As another factor affecting the kinetics of cellulose hydrolysis process, enzyme decay factor is incorporated into the model as the typical first order decay process. We consider two different processes for cellulases losing activity during hydrolysis in order to better understand the impact of enzyme decay on hydrolysis. Numerical simulation results are presented to investigate the phenomenon of hydrolysis rate slow-down commonly observed in experiments. Improvement of the predictive capability of the new model over previous one is clearly demonstrated by comparing the simulations with experimental data. By considering all the possible hydrolysis rate slow-down factors, the simulation results can agree with the experimental data very well, showing that our model is capable to fully capture the rate decrease of cellulose hydrolysis.