A new multi-agent based congestion evacuation model is proposed in this paper to simulate the pedestrian evacuation process in stadium with or without obstacles, in which each agent's state can be normal, being overtaked and dead. In this model, all the pedestrians are divided into four kinds and each kind has six different classes of competitive ability. The individual action direction is affected by their competitive ability, the distance to the exits and the occupant number and density within the view field of the agent. In the simulation, we present the congestion and death phenomenon as well as the effects of obstacles in evacuation process. We also add a virtual leader to regulate the evacuation effectively. Simulation results show that the proposed model can reproduce exactly the real evacuation process in stadium.