Abstract: Study on the law of oil vapor leakage and diffusion in inner floating roof tanks is of great significance for strengthening environmental pollution control and ensuring tank farm safety. The wind tunnel test platform was established to test the effects of wind speed and floating plate position on evaporation loss rate of small inner floating roof tank, and the distribution laws of wind field and concentration field were investigated. Based on CFD numerical simulation, the UDF was used to introduce environmental wind, the numerical model of oil vapor leakage and diffusion from inner floating roof tank was established, and the feasibility of the simulation was verified by wind tunnel experimental data. The distribution law of wind field and wind pressure outside the inner floating roof tank, as well as the influence of wind speed on the flow field distribution and the diffusion concentration of oil vapor in the inner floating roof tank, was emphatically discussed. The results show that the lower the floating plate position and the higher the wind speed, the faster the evaporation rate will be. The static pressure distributed on the tank wall is as follows: highest on windward wall, medium on leeward wall and lowest on the two side walls. Under different wind speeds, the distribution of oil vapor on the tank is symmetrical. The lower the wind speed, the higher the oil vapor mass concentration will be. The oil vapor concentration at the gap between floating plates is the highest, leaving hidden dangers of safety and environmental pollution. The research results are of reference value for the design, operation and maintenance of the inner floating roof tank and environmental protection and safety management.