Abstract: China's urban distribution network is facing the pressure of insufficient power supply capacity. The emergence of medium voltage DC (MVDC) distribution mode provides a new idea and method for urban distribution network transformation. Considering the reliability and adaptability, bipolar three-wire connection mode is selected as the connection mode of MVDC distribution network. Firstly, the rated voltage relationship between AC and DC distribution network is determined by considering the over-voltage level of the AC and DC lines. Then, the power supply capacity of MVDC and MVAC distribution networks is deduced from three aspects of voltage loss, power loss and power supply capacity, and the universal model of power supply capacity for AC and DC distribution network is built. Finally, by taking commonly used medium voltage cable YJV-300 as example, analysis shows that the power supply capacity of MVDC distribution network is significantly superior to that of MVAC distribution network. In particular, the power supply capacity of the DC distribution network is studied when monopole grounding fault occurs, and it is found that the DC power distribution network also has a certain advantage on power supply capacity by comparing to AC distribution network.