In  order  to simplify  the complex  calculation  and  analysis procedure  in  simulation  analysis on  LNG  tank  leakage and  gas diffusion, selected  is an appropriate gas diffusion  model  and  applied  is the  Matlab program  for conducting rapid  simulation  of methane gas diffusion and drawing a gas diffusion concentration distribution diagram so as to predict explosive and hazardous areas probably  formed in downwind methane steam diffusion and to simulate effect of such factors as wind speed, ground  roughness and LNG leakage rate on methane steam diffusion. Study results indicate that if the wind direction is in line with the diffusion direction, diffusion  distance and hazardous areas show a trend of decrease along with wind speed and ground roughness increase, and diffusion distance and hazardous areas show a trend of increase along with leakage rate increase.