Abstract-In order to quantitatively and systematically explain the accident occur process and assess the risk for the complex system, this paper proposes a new accident-causing analysis model, i.e. perturbation-safety region (P-SR) model. In this model, the safety region definition is introduced for the quantitative description of the system safe status; also the change process of the system risk is analyzed. The four relative parts included in this model are described in details, such as the risk resource part, the perturbation part, the alarm and system change part, and the accident part. Finally, the proposed model is applied to railway transportation system, and the Wenzhou train collision is systematically analyzed, also the specified control measure for the train emergency dispatch is demonstrated.