This study simulates the temperature field distribution inside the transformer under different ambient temperatures. In order to explore the insulation performance of the transformer under extreme ambient temperatures, finite element simulation was used to simulate the distribution of the temperature field inside the transformer at ambient temperatures of −40 ℃, −20 ℃, 0 ℃, 20 ℃ and 40 ℃. The study found that when the ambient temperature is too low, the convection heat dissipation capacity of the transformer oil will be weakened, thereby increasing the temperature inside the core; when the temperature is too high, the temperature field distribution inside the transformer will be more uniform, but the life of the insulating paperboard will be reduced. The temperature rise trend inside the transformer remains consistent under various ambient temperatures, and the hot spot temperature can reach up to 106.4 ℃. The temperature at each moment shows an obvious linear relationship with the ambient temperature. The temperature ranges at various locations inside vary greatly, with the temperature gradually increasing from bottom to top and gradually decreasing from inside to outside.