The electrical and thermal characteristics of a transformer determine its load capacity and usable life, and excessive hot spot temperature accelerates the thermal aging of the insulation system, resulting in a reduction of its usable life. Taking an oil-immersed transformer as an example for research, by implanting fiber-optic temperature measurement probes inside the windings, the distribution characteristics of hot spot temperatures of high and low-voltage windings are measured and analyzed under rated operating conditions. According to the technical parameters of the transformer, the simulation calculation model is established, combined with the actual temperature rise test, to study the hot spot temperature of high and low voltage winding with time and ambient temperature change rule during different short-circuit faults within 2 Seconds. The results show that: transformer outlet short circuit fault and temperature rise test conditions of the winding hot spot temperature distribution law are different, in the outlet short circuit fault within a short period of time, high, low-voltage winding temperature with the short-circuit time of the highest temperature are a linear increase, while the top layer of the oil temperature is almost unchanged. With the rise of ambient temperature, the transformer winding hot spot temperature increases linearly, posing a serious threat to the safe operation of the transformer.