Abstract: Nowadays multi-terminal high voltage DC（HVDC） networks have been drawing more interests because of their flexibility, reliability and efficiency. HVDC circuit breaker is one of the most important equipment to maintain the stable operation of the DC grid. When it comes to the high voltage area, the reliability and efficiency of traditional mechanical and hybrid circuit breaker are not satisfied. So, a new circuit breaker topology with coupling reactor was proposed, the working principles as well as the advantages of which were analyzed in detail. A 160 k V mechanical HVDC circuit breaker had been designed, developed, tested and put into operation, which proved the reliability of the topology. Then, improvements are put forward, to meet the requirements of 500 kV DC grid. The PSCAD simulation model is built and the simulation results verify the function of the modified DC circuit breaker topology.