Abstract: Event Sequence Diagram (ESD) method is usually used to analyze the accident＇s development and consequences. However, it is quantitatively insufficient to control the model scale and lack of modeling capability. Fo r the complicated system, model purely produced by ESD method is often too complicated to be intuitive. A hybrid approach is employed which combines ESD with Fault Tree method to produce the model. In this way, it can make full use of the advantages of fault tree analysis techniques and the produced model is more concise and intuitive. This paper explores the application of ESD_FT method in the marine reactor accident analysis, and a new evolving ESD event by inner FF is proposed, and the model marine reactor water-loss accident analysis is established. Finally, happening probability of accident is obtained. The results show that ESD_FT method is more effective and applicable for the accident analysis.