Abstract: Numerical simulation was implemented to study the phenomenon of instantaneous release of heavy gas using computational fluid dynamic method so as to do research on the distribution of concentration of heavy gas and on how to apply the distribution characteristic to industrial safety. Numerical simulation method could not only simulate the physical process of heavy gas release but also predict the distribution of concentration both at space and time with high reliability, results of simulation were compared with both theories of heavy gas dispersion and with observation results from large-scale field tests. Results of simulation can quantitatively predict the accurate time when dangerous concentration is reached and predict how long it will stay in certain sites, for specific time, space distribution of dangerous concentration can be provided. Risk of poisoning in near-source zones and far-source zones can be equally provided that toxic threshold is low enough.