Multi-winding dry rectifier transformer is an important equipment for high voltage power supply in Tokamak heating system. Its excellent performance is directly related to the output quality of high voltage power supply. Carrying out research on power loss and heat dissipation of transformers, reducing the performance impact of transformers due to temperature rise, is very important to ensure the good working condition of the transformer. In this paper, the relationship between thermophysical properties and temperature is fitted by MATLAB. The convective heat transfer and thermal radiation of the transformer are analyzed and calculated by the equations. In the case of natural convection and heat radiation of the air, the temperature of the transformer cannot be controlled within a temperature range that satisfies the performance, and the temperature rise is about 200 ℃. In the case of forced air convection, the good heat dissipation of the transformer is realized, and finally the forced air cooling at a wind speed of 2 m/s is achieved, and the temperature rise of the transformer is less than 75 ℃, ensuring the good working condition of the transformer. The article further uses ANSYS to analyze the temperature field distribution of the transformer. Forced air cooling reduces the overall temperature and allows heat to be released to the surrounding atmosphere more quickly, reducing the damage of the transformer under high temperature.