Abstract: For passive nuclear power plants, such as AP1000, the radioactive aerosols in containment are removed by natural processes after accidents. This method has the advantage of high reliability. However, it is very complicated to analyze the behaviors of aerosols in natural processes. The dominant processes include coagulation, sedimentation, diffusionphoresis and themophoresis. The aerosol natural removal for AP1000 was analyzed in this study. The results indicate that diffusionphoresis makes the biggest contribution to aerosol removal while the themophoresis and sedimentation are the next two important processes for LOCA. After LOCA, the aerosol natural removal coefficient in containment of AP1000 is about 0.4-0.9 h^-1, and it does not change much after core uncover 5 h. Based on RG1-183, with atmospheric dispersion factor and aerosol removal coefficient given in this study, the calculated offsite and control-room dose for AP1000 after LOCA meets the regulation requirements in 10CFR50.