Abstract: Simulation of atmospheric dispersion of radionuclides is one of the main contents of radioactive consequence assessment and emergency decision to nuclear accidents. Gaussian plume model is simple and convenient, and it has been applied widely for assessing the radioactive consequence of nuclear accidents. The atmospheric dispersion code SDUG of radionuclides was developed based on the Gaussian plume model considering gravitational settling of particles, rain washing and the decay of radioactive species. The SDUG can calculate the radionuclide concentration distribution in different meteorological and topographical situations for instantaneous and continuous point sources under normal and accident conditions. The results of SDUG are in good agreement with the reference code values and can meet the requirements for early nuclear emergency and consequence assessment.