Fateful stampede accident has become one of hot spots in public security field because of its sudden and serious consequence. Actual cases show that crowding is not a sufficient condition for fateful stampede accident, but a necessary condition. Some emergencies play a role of trigger in stampede accident, such as fire, explosion, individual injury, earthquake, etc.Evolution mechanism of fateful stampede accident is discussed based on graphical evaluation and review technique (GERT) in the paper. Escape panic caused by emergencies greatly increases the risk of stampede accident. In the presented model, risk of fateful stampede accident is measured in terms of the difference between "desired velocity" and "actual velocity" of crowd. Finally, a GERT model is set up to describe the evolution mechanism of a fateful stampede accident at Miyun county.K�words-fateful stampede accident, evolution mechanism, GERT I.