Oil-immersed transformer is the key equipment of power transmission, the fire caused by its failure will cause huge economic losses. The aim of this study is to investigate the combustion characteristics of oil-immersed transformer fires under different environmental conditions, and the effectiveness of high-pressure fine water spray on transformer fires under different parameters. Numerical simulation of transformer fires using PyroSim software simulation of high-pressure fine water mist fire extinguishing effect -parameter optimisation, focusing on the combustion characteristics of transformer fires at different ambient temperatures (-5℃, 0℃, 5℃, 10℃, 20℃) and wind speeds (0 m/s, 1 m/s, 2 m/s, 4 m/s) and the suppression effect of high-pressure fine water mist on transformer fires at different spray flows (0.3 L/min, 0.6 L/min) and ambient wind speeds (0 m/s, 1 m/s, 2 m/s, 4 m/s). The simulation results show a negative correlation between the temperature variation above the flame and the spatial height. Changes in ambient temperature with insignificant changes in flue gas concentration and mean changes in flue gas temperature between 800℃ and 900℃. Changing the ambient wind speed deflects the flame along the wind direction and has a greater effect on the temperature field distribution above the flame. When the spray flow rate is 0.6L/min, the high-pressure fine water mist system has a better cooling effect on transformer fires. This study has shown that high pressure fine water mist systems can effectively extinguish oil-immersed transformer fires under the appropriate parameters. However, the effectiveness of the high-pressure fine water mist in extinguishing fires is reduced in the presence of increased ambient wind speeds. This paper provides the corresponding theoretical support for the development.