With the popularization and application of auxiliary transportation devices such as diesel monorail cranes and trackless rubber-wheeled vehicles in underground coal mines, the frequency of transporting and refilling diesel fuel in underground mines is getting higher and higher, leakage of diesel fuel and volatile diesel vapor during transportation and refueling will pollute the underground air environment, and may cause combustion and explosion accidents in serious cases. In this paper, for the environmental characteristics of diesel transportation and refueling process in underground coal mine, we constructed the evaporation and diffusion model of leaked diesel in underground fluid environment, established the prediction method of peak diesel vapor volume fraction based on wind speed and evaporation rate, investigated the distribution law of diesel vapor volume fraction under the conditions of different ambient wind speeds and diesel evaporation rates, and put forward fire prevention and explosion-proof measures for the mixed diesel vapor-gas environment in underground coal mine. The results show that in the underground flow environment, diesel vapor diffusion presents obvious subsiding, layering and segmentation characteristics, and the wind flow has a promoting effect on diesel vapor diffusion. When the diesel was leaking for 20 s, the vapour spread to 10 m downwind of the leak, and when the diesel was leaking for 40 s, the vapour spread to 15 m downwind of the leak, and when the diesel was leaking for 70 s, the volume fraction of diesel vapour in the chamber reached a peak and tended to stabilize, and the peak volume fraction of diesel vapour was located at a point 1 m downwind of the leak. Measures such as lowering the ambient temperature of the chamber, reducing the leakage area and increasing the air velocity can be taken to prevent the diesel vapour-gas mixture from burning and exploding.