Abstract: Coupling model of thermal-hydraulic, fission products behavior and radiological consequences assessment was constructed. Based on high-pressure core melt severe accidents of SB-LOCA, SGTR, SBO, and LOFW, the influence of reactor coolant system （RCS） depressurization on ex-vessel release of fission products was studied, including mitigation effect on ex-vessel release of fission products and other negative effects. It is shown that RCS depressurization can mitigate ex-vessel release of fission products for high-pressure core melt accident sequences, while airborne activity in the early phase with RCS depressurization is higher than that of the base cases without RCS depressurization. The research results can give support to establish severe accident management guideline.