Abstract:To explore the development direction of highreliable distribution network in future, it was the first time toresearch the reliability of medium-voltage flexible DCdistribution network in depth.With the development of voltage source inverter，flexible DC transmission and distribution technology presents the advantages of no commutation failure problem when supply power to no source area. the reliability of DC distributionnetwork would be close to that of AC distribution networkgradually and even higher than that of AC distribution network.It provides good technical support for the poor power supply ability in super-large city. The article analysis the supply situation in large cities and the need of Flexible DC transmission and distribution network in super-large city. Focuses on t protection configuration and action strategy on flexible DC transmission and distribution network in megalopolis. According to electrical wiring position the relay configuration is divided into three parts such as AC switch yard protected areas、protection zone converter and DC transmission line protection zone. According to the characteristics of each district there are different fault protection functions. There is certain reference value on protection configuration and action strategy on Flexible DC transmission and distribution network in megalopolis.