Abstract: In order to solve the problem that the conventional differential protection for high voltage direct current（HVDC） transmission lines can’t respond to internal faults quickly, a novel differential protection scheme was proposed in this paper. After voltage and current signals at both line ends are processed by the same low-pass filter the cut-off frequency of which is low enough, then the voltage distribution along the line can be regarded as linear distribution. The distributed capacitive current can be calculated by integrating the linear distributed voltage. After compensating for this current, the new differential criterion can be implemented. If the cut-off frequency is set lower, the distributed capacitive current can be ignored. In this case, the fault line can be selected by comparing the filtered differential current of both lines. A ±800 k V Yun-Guang HVDC transmission system was built to test the performance of the new protection scheme. Comprehensive simulation results show that the proposed method not only can detect internal faults and select the fault lines correctly and quickly, but also can respond to internal faults with high ground resistance.