Abstract: The static security distance analysis method is one of the important methods to evaluate the security margin of power grid operation. The traditional assessment method with the shortest security distance as the index does not consider the evolution law between different operation sections, which leads to the conservative assessment results. In this paper, a static security margin assessment method is proposed, which takes into account the timing characteristics of power system operation. By extracting the characteristics of historical load variation, the timing law and extension direction of power load are obtained. The static security margin can be evaluated according to the obtained load extension direction. The IEEE 9 node standard example and the actual grid measurement data over a certain period of time are used to verify the effectiveness and feasibility of the proposed method. The results show that the proposed method can provide security margin information reflecting the actual operation law of the power grid, avoiding the problem of relatively conservative assessment results of traditional methods, and provide a new basis for improving the optimal dispatching operation of static security of complex power grid.