The power grid dispatching automation system consists of many subsystems, and each subsystem suffers different risk attacks. As a result, it is difficult to comprehensively detect the network security risks of the power grid dispatching automation system, and the security defense effect is poor. In order to solve this problem, the security defense technology of power grid dispatching automation system based on hierarchical protection is proposed. This paper analyzes the current security protection status of power grid dispatching system, and establishes the security protection system of power grid dispatching system from four aspects of terminal security, network security, dispatching security and data security by using the hierarchical protection idea. The analytic hierarchy process (AHP) is introduced to construct a security defense model composed of criterion layer, target layer and index layer, calculate the consistency index of the model layer by layer, and then, complete the consistency check of the model as a whole, so as to realize the security defense of the power grid dispatching automation system. By setting up an experimental environment and conducting experimental comparisons with other algorithms, the results show that the proposed method has a very ideal security defense effect and can defend against three different types of attacks at the same time.