With the continuous application and popularization of distributed energy,DC power distribution will become the mainstream form of future power distribution system. As a new type of power distribution system,the overvoltage and insulation coordination of flexible DC power distribution urgently needs further research and improvement. The addition of medium-voltage DC circuit breakers has also led to fundamental changes in the operating overvoltage transient characteristics of the system. It is necessary to analyze the operating overvoltage distribution characteristics and insulation coordination of the flexible DC distribution network with DC circuit breakers. Firstly,the electromagnetic transient simulation model of ±10 kV ring-network flexible DC power distribution network is constructed,and the protection action scheme based on DC circuit breaker is designed. Then,the ±10 kV ring network flexible DC power distribution system is simulated and analyzed for operating overvoltage,horizontal spatial distribution characteristics of its amplitude and the decisive working condition of the maximum overvoltage at key positions are obtained,insulation coordination scheme of the ±10 kV ring network flexible DC power distribution system is proposed. Finally,the simulation analysis of the transient induced overvoltage of the DC cable sheath under the influence of the action of the DC circuit breaker is carried out. The results show that the addition of DC circuit breakers improves the reliability and flexibility of DC distribution network,and the layout of arrester and cable metal shield protector is further optimized,which is of great significance to the design of insulation matching scheme of flexible direct distribution network of ring network.