Abstract: With the increasing need of nuclear power, almost all countries who want to build new nuclear power plant take the generation Ⅲ technology as their first choice. The main reason is that the safety of generation Ⅲ technology has been improved greatly than generation Ⅱand Ⅱ+ technology. The passive safety technology is introduced by AP1000 and it is one of the best in generation Ⅲ technologies. The representative passive containment cooling system of AP1000 and containment spray system of generation Ⅱ nuclear power plant were compared in the paper and analyzed using probabilistic safety assessment method. The reasons of passive safety system possessing comparative advantages were obtained by the concrete calculation.