In this paper, a computational evacuation discrete time model(EDTM) has been presented to analyze the building egress evacuation time problem with previous works, and discusses the advantages of the use of the modified model over the use of the previous model. EDTM uses crowd flow theory and discrete computational methods to identify various width of egress that are available to the occupants for movement,  which is more accurate and practicable because the crowd flow rate is variable, while the crowd flow rate as the function of crowd density based on the empirical relations between density and velocity of crowd movement. A case of stadium stand egress is chosen for the validity of EDTM, and a comparison of EDTM with previous model and computer simulation indicates that both the EDTM and the simulation curves are found to give better predictions than the previous model. Based upon the results, EDTM shows great value in dealing with stadium,  especially the2008Beijing Olympic stadium, evacuation time calculation, egress performance design, selecting and optimizing of routes and so on.