The synthetic risk assessment method incorporating the severity and the possibility is used to identify the catastrophic event sequences in power system. The weight setting of each severity index is determined by the proposed entropy weight method. Comparing with traditional methods, the entropy weight method can determine the weight coefficients objectively. The simulation results for the WSCC-9 buses system have proved the validity of the proposed method. This method can be used in the practice power system. © (2012) Trans Tech Publications, Switzerland.