The intensity and type of partial discharge in distribution transformers are directly related to the degree of insulation degradation, Therefore, accurate identification of the type of partial discharge is the key to ensuring the stable operation of distribution transformers. At present, most experiments on partial discharge failures rely on defect models to simulate various partial discharge phenomena. This paper uses the finite element method (FEM) to analyze the electric field distribution of the four commonly used defect models and the free bubble defect model under high voltage. The existing surface discharge model was optimized to reduce the size of the breakdown electric field, increasing the surface electric field by 4.8 times, allowing for more accurate simulation of surface discharge defects. At the same time, the actual model of the transformer is constructed in this paper to study the propagation of the acoustic emission signal generated by partial discharge. Through theoretical analysis, the four-point positioning method and the optimization of sensor position can realize the positioning of partial discharge.