After the transformation of AC cable into DC operation, it is very important to conduct temperature and electric field simulation on the power cable joint and study its temperature distribution and electric field intensity to accurately evaluate the power supply capacity. At present, researches on the DC transformation of AC cable almost focuse on the cable body, and there are few researches on the cable joint. In this paper, the 3D simulation model of 10 kV three-core cable joint which is commonly used in the urban distribution network is established, first, the ANSYS heat-electricity coupling module is used to simulate temperature field of previous statement 3D model in which the contact resistance coefficient is four and the temperature distribution is analyzed. Then, the influences of contact resistance, and air convective heat transfer coefficients on cable joint temperature are studied. At last, the DC electric simulation of cable joint is conducted, and choose the DC current capacity and suitable DC voltage according to the temperature and electric simulation, the maximum transmission power is compared with AC cable joint. The results show that the power transmission capacity of AC cable joint is improved after the DC transformation.