The shunt large capacitances on both sides of voltage source converter based high voltage direct current（VSC-HVDC）transmission lines，will rapidly discharge to the fault point when a fault occurs，and the system side reactance can be equivalent to the shunt large capacitance in the model of high frequency fault component.According to this characteristic of VSC-HVDC system，a novel principle of pilot protection for VSC-HVDC transmission lines based on shunt capacitance parameter identification method is proposed.The protection principle using time-domain algorithm can distinguish internal and external faults by identifying the capacitance parameters at both ends of transmission line.The capacitances at both ends can be accurately identified simultaneously when an internal single pole ground fault occurs.But the capacitances at both ends cannot be accurately identified simultaneously when an external fault occurs.According to this characteristic，a pilot protection criterion is constructed.The theory analysis and simulation results show that the method is not affected by transition resistance，fault type，fault location，control mode and line type，and it can identify internal faults and external faults reliably and rapidly in various situation.In addition，the method can be implemented easily with simple computation，having certain practical value.