The invention relates to a defense method for multi-stage network attack of a power information physical system, comprising the following steps: firstly estimating the modes and resources of the attack and defense sides, adopting a staged offensive and defensive process, and determining the total number of stages of attack and defense; secondly, sequentially calculating the load shedding values ofall possible attack and defense combinations in the next stage using the optimal load shedding algorithm to obtain the potential return of each attack and defense strategy in the current stage; stipulating that the attacker and the defender are simultaneously operated, and obtaining the return matrix of the action of both parties based on the game strategy; getting the Nash equilibrium point of the game by integrating multiple stages, and constructing a decision table to provide guidance for the defense party's active defense method. The invention provides a defense method for coping with multi-stage network attacks, and comprehensively considers resources and means of both offense and defense parties, and may guide the establishment of a grid security defense mechanism.