Abstract: The passive safety system of AP1000 is a new type of safety system, which is different to the second generation nuclear power plant in principle and system layout. There is no actual operation experience of AP1000, therefore, the design principle of AP1000 still need be further verified and analyzed. This paper uses JTopmeret and THEATRe modeling software to carry out simulation on passive residual heat removal system (PRHRS) and core made tank (CMT) system of AP1000. The simulation object is to verify the feasibility and validity of PRHRS and CMT system during accidental conditions. The simulation results show that PRHRS and CMT system can discharge decay heat timely and effectively and guarantee safety of reactor core. The conclusions have reference value in helping operation of AP1000.