Abstract: The assessment about environmental safety of gaseous tritium is an important issue in the fusion nuclear safety field. Based on the solution of atmospheric turbulent diffusion model, a module of TAS to calculate tritium atmospheric distribution for acute and chronic releases was developed by using MATLAB. A series verification was finished, including the comparisons with the HotSpot3.0 developed by LLNL, UFOTRI developed by KfK, experimental results at Chalk River and Savannah River Plant. The results show that TAS is effective for the simulation of gaseous tritium distribution in the atmosphere. The main features of plume and puff model were discussed and a method for simulating nuclear accident emergency was proposed.