Abstract: In order to estimate the potential offsite effect caused by severe accidents of AP1000 nuclear power plant, radiation dose risk was quantified, which takes into account six representative release categories. Atmospheric transport with airborne radioactive material was simulated by MACCS code. The results show that acute red marrow dose risk at the site boundary is 1.96×10^-7 Sv/(reactor•year), which mainly results from containment bypass release (BP). The early health effect risks are 10^-10-10^-9 Sv/(reactor•year), and the risks decrease obviously with the increase of distance from reactor. Population whole body effective dose risk is 6.94×10^-4 person•Sv/(reactor•year), and the corresponding cancer fatality risk is quite low. The study result also indicates that timely evacuation after the nuclear accident can reduce public dose risk significantly.