Abstract: The forces between evacuees and environment have an critical influence on the evacuation dynamics of crowds. Based on the analysis of current related models, an improved cellular automata model is proposed, which takes into account those forces by adopting both overlappable multi-grid cell and modified floor field. Comparative study of crowd dynamics against exit width and crowd density is carried out for the improved model and the traditional. The results reveal the necessity and rationality of involving crowding forces into the cellular automata model for evacuation simulations. This work is helpful to those researches of crowd dynamics by simulations.