Flexible multi-terminal DC system has significant advantages in terms of renewable energy and island power supply. To ensure the safe operation of flexible DC grid, it is necessary to research and develop a high-voltage DC circuit breaker capable of breaking the fault current in milliseconds. In this study, a low-stray inductance power electronic branch series topology is proposed based on the breaking parameters of the high voltage DC circuit breaker used in South Australia ±160 kV flexible DC system with the introduction of high voltage DC circuit breaker topology design based on coupled negative voltage circuit. After the checking analysis of key components and series structure design of valve string in power electronic branch, the modular design of power electronic branch valve string is completed, and after the verification of design strength of each parts by seismic analysis of integrated circuit breaker, the designing of ±160 kV high voltage DC circuit breaker prototype based on coupled negative voltage circuit is completed.