After analyzing the demand of de-lamination and sub-area power supply in power system, an index system to evaluate load dispatching in operating and planning of power grid is established by considering the power system economy, security, reliability and especially the risk of electrical safety incidents. The index first considers the risk of electrical safety incidents, and can reflect the real demand of load dispatching in operating and planning of power grid comprehensively. The indexes values of different load dispatching schemes can be obtained through calculation, and then the method of Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) is used to solve the multi-objective optimization problem. It is proved that this index system can meet the needs of load dispatching in actual power grid by simulation. And the index system and the optimization method can provide dicision support for power system operating and planning.