The invention discloses a circuit cluster-based method for analyzing a grid cascading failure, belonging to the technical field of safety protection of a power system. The method comprises the following steps of: applying a Bayes network failure tree theory to cascading failure analysis based on a distribution failure probability model of a self-critical circuit cluster and establishing a probability analysis model for a grid cascading failure based on cascading failure probability analysis of the self-critical circuit cluster in combination with the probability characteristic of a cascading failure developing stage; and through simulating a cascading failure process, performing risk assessment on the cascading failure by using a system load loss index and analyzing weak links of a system. By adopting the method, foundations are provided for a prevention strategy for further research on the reduction of cascading failure risk.