Most serious breakdown faults of cross linked polyethylene(XLPE) cables in distribution network occur at cable joints,which are mainly caused by process defects in the manufacturing and installation of cable joints. In this paper,the charge simulation method is used to study the characteristics of electric field distribution near four typical defects of cable joints,namely,air gap,water film,metal debris and metal breakout. The electric field calculation and random walk theory are combined to analyze the distribution of electrical tree caused by several defects. At the same time,the actual electric field distribution around the sample of XLPE cable joints in the distribution network with defects is measured,and the measured results are compared with the calculated results. The results show that the electric field measurement method can directly and effectively identify the types of internal defects of cable joints,and the electric field distortion caused by conductive defects is more significant than that caused by air gap and water film defects. When the electric field distortion caused by defects is greater than the critical electric field value,the electric tree will develop. The track length of the electric tree development is positively related to the field strength. The electrical tree caused by conductive defects is more likely to develop towards the cable core,which is more likely to cause the breakdown of XLPE insulation.