Abstract: A kind of hybrid parallel algorithm of assessing risks of power system based on OpenMP and MPI is presented in this paper to improve the efficiency of the large-scale numerical calculation for non-sequential Monte Carlo Simulation in the analysis of transient stability. The Monte Carlo sampling points are allocated in multiple processes of PC cluster based on MPI method by using dynamic programming, and the loop of analyzing and processing system failures is decomposed based on OpenMP by using of multi-thread parallel computing model in each process. The models testing and data analysis show that this algorithm has expectant parallel calculation efficiency with good accuracy. The normal PC cluster can achieve up to 3.28 times speedup, and hybrid cluster can achieve up to 5.06 times speedup by using of proposed algorithm, which verifies its effectiveness.