To study the diffusion process of liquefied natural gas tank gas phase leakage, we can get the laws of wind speed, leakage height and obstacle factors on the leakage and diffusion of LNG tank. In this paper, FLACS is used to build the tank leakage diffusion model. With the help of Flowvis, the post-processor of FLACS, the design of visual gas diffusion model is realized. Two-dimensional and THREE-DIMENSIONAL graphics output operation of various variables is performed, and automatic video generation and data analysis are completed. The results are as follows: when the wind speed increases from 2m/s to 8m/s, the maximum downwind diffusion distance of the 1/2LFL cloud increases; when the wind speed is larger than 8m/s, the maximum downwind diffusion distance of the 1/2LFL cloud decreases with the increase of the wind speed. With the increase of leakage height to 8m, the farthest downwind diffusion distance of gas cloud decreases gradually. After 60 s of leakage, the maximum diffusion distance of 1/2LFL gas cloud is 116 m, which is 14 m shorter than that of single tank leakage. The results show that the wind speed will increase or decrease the diffusion of gas phase leakage due to the change of actual data. The higher the leakage height is, the lower the gas phase leakage distance is. The existence of obstacles to a certain extent obstructs the diffusion of gas cloud downward wind direction, reducing the explosion damage range.