The essence of DC circuit breaker (DCCB) is to break the fault current. The electrical parameters in transient breaking process are the core expression which determines the breaking characteristics of circuit breaker. In this paper, based on the analysis of DCCB topology, the transient process of breakers is divided into three stages. The transient characteristics of the circuit breakers in the breaking process are analyzed by establishing the fault equivalent circuit for the DC grid with DCCB and the system level equivalent circuit for breaker at different breaking transient states. Combining the parameters of the circuit breaker with the parameters of the DC system, the two flow process of the circuit breaker is analyzed in detail. The mathematical model of breaking current, transient voltage and breaking time is established, and the calculation expression of the breaking current and the maximum transient voltage in the whole process of breaking the circuit breaker is derived. The influence of circuit breaker parameters on breaking performance is analyzed. By using PSCAD/EMTDC, a system level hybrid DCCB simulation model is built to verify the transient model of circuit breaker and the influence of parameters selection on the interruption performance of the circuit breaker. This work is supported by National Key Research and Development Program of China (No. 2017YFB0902401) and Science and Technology Department of Jilin Province (No. 20160307014GX).