In order to promote the development of urban Energy Internet and meet the new needs of urban energy reform, the construction of urban Energy Internet based on flexible DC distribution network is proposed. Then, the key technology analysis on the core network of the physical infrastructure layer of the urban Energy Internet, namely the flexible DC distribution network, has been carried out. Then a complete set of technical system including planning and design, key equipment development, operation control, fault protection and other of the multi-terminal flexible DC distribution network is established, which provides strong technical support for the planning and construction of flexible DC distribution network. Finally, the design and analysis of the flexible DC distribution network demonstration project have been carried out, the overall construction plan of the project has been proposed. And Zhuhai Tangjiawan three-terminal flexible DC distribution network project with the largest capacity and highest voltage level in the world has been successfully put into operation, which lays a solid foundation for advancing the construction and operation of flexible DC power distribution technology in China, providing support for the development of the urban Energy Internet and building an international energy transformation city.