Affected by strong earthquake and tsunami in east Japan, large amounts of radioactivity have been emitted from Fukushima Nuclear Power Plant since 12 March 2011. In this paper，Models 3/CMAQ is used to simulate the radioactive leak under ideal conditions. The results show that the radioactive releases mainly affect the vicinity of Fukushima and the northwest of the Pacific Ocean, the radioactive releases can disperse to higher altitudes, and the concentration of radioactive releases decreases exponentially with height increasing in source region. Moreover, radioactive releases have trivial effect on China through northeastern and eastern paths; and Models 3/CMAQ is capable of simulating radioactive leak accident.