The main function of DC reactor in the VSC-HVDC system is to suppress the rate of rise and peak value of the fault current, and to isolate the fault of the DC side with DC circuit breaker. The inductance value of DC reactor determines the operational safety and system stability of the inverter,it plays an important role in the excecution of control and protection strategy of the entire system. At present, there is no relevant design criteria and method of calculation for the parameters of the inductance value of DC reactor. For the different parameters of the VSC-HVDC system,it’s very important to search for a reasonable method for determining the inductance value of DC reactor. This paper analyzes the generation mechanism of short-circuit current of half-bridge converter,and the parameter value calculation is based on the typical case of medium voltage flexible DC. Double-ended VSC-HVDC system is bulit in PSCAD/EMTDC electromagnetic simulation software to verify the correctness of the design method by simulation.