The modified floor field cellular automata model is used to simulate the pedestrian evacuation in rooms which are discretized into squared rhombus cells. This discretization can effectively stop pedestrians to move against walls or obstacles. The pedestrian transition probabilities from one cell to neighbor cells are computed by considering various factors influencing evacuation. Simulation results show that the pedestrian distribution nearby exit is basically the same as that indicated by the experimental snapshot, the evacuation time increases almost linearly with exit width, and the flow rate from exit is close to the one observed from experiment.