Based on analytical method and stochastic simulation method, an assessment model of cascading failure in power grid based on hybrid method is proposed. A model for calculating the probability of failure removal of the relay protection system considering the effect of major protection and remote backup protection is established by using Markov space theory. The expected fault of line is screened rapidly by using the index of contingency behavior and the concentric relaxation method, and it is divided into different initial fault conditions in order to determine the set of initial fault. The follow-up fault is simulated based on reliability model of generator, line and load in real-time operating conditions. The index of severity of cascading failure path is defined based on risk theory in order to assess the weak links in the system. The results of simulation show that the model is rational and effective.