The evacuation efficiency of building plans is of obvious importance to the public safety. The complexity of building plans, however, makes it difficult for the efficiency evaluation. This paper presents a computational model AutoEscape, which can simulate the evacuation process for any given occupant distribution in buildings. Designed as an extensible multi-level structure, the model constructs the geometry level and occupant level and establishes the interactions between levels. The GIS-based environmental analysis is realized to automatically generate the geometric representation and formulate the cognition of agents. The multi-agent based technology is employed to simulate the crowd behaviors with autonomously acting individuals. A visualization component, which provides 3D free observations for the simulation process, is developed on the platform of OGRE and integrated into the system interface in form of ActiveX control. Finally, a case study has been conducted and the results have been compared with the results of an existing model to show the reliability and capacity of AutoEscape simulation.