Abstract: For the development of large regional power grid and the issues of security and stability, the inherent mechanism of large area power system blackouts and cascading failures are studied based on the complex network theory. From the topological models and vulnerability indices, various assessment methods are analyzed. It is pointed out that applying the complex network theory to the vulnerability assessment of power systems is still inadequate currently. The essential difference between power grid and other complex networks is the bottleneck problem of the research. It’s suggested that how to improve the assessment models accuracy to reflect the essential characteristics and operating status of the grid is emphasis of the study in future.