The invention discloses a method for evaluating vulnerability of a power system to a network attack. The method comprises the steps of evaluating a communication network attack success probability, evaluating power system node influencing factors and calculating comprehensive vulnerability, thereby evaluating the vulnerability of the power communication system to the network attack. By adopting a generalized stochastic Petri network to model the communication network, the spreading process of the attack under protection ways such as firewall, password and the like can be simulated, and the probability that a substation or a control center is in failure due to attack success is calculated; by adopting the influencing factors, the importance of each substation to system stable operation can be characterized; and therefore, the method gives consideration to the characteristics of the communication system and the characteristics of the power system, and is beneficial to researching the interactive influence characteristics of the power communication system.