In order to study the influence of DC magnetic bias on transformer temperature failure. In this paper, a three-dimensional model of oil immersed converter transformer is established, the loss under DC bias is calculated, and the temperature distribution under DC bias is simulated by the finite element method. The temperature failure of the transformer under different working conditions is analyzed. It is concluded that when the converter transformer is subjected to more than 10A magnetic bias current for a long time, it will lead to local overheating and reduce converter life.