Abstract: Aiming at the difficulty of differential protection in high-impedance-fault identification and easily disturbed by interferences,such as noise,external short-circuit faults and abnormal data,a protection scheme for flexible DC distribution lines based on improved differential current function is proposed. The improved differential current function enhances the difference of inner and external shortcircuit transient characteristics,which is conducive to the identification of high-impedance fault,and avoiding the influence of external fault on the reliability. The improved Hausdorff distance algorithm based on the Same convolution can effectively suppress the interference of abnormal data. Finally,the fault zone and fault type are identified by the cooperation of improved differential current function and its convolutional Hausdorff distance. Simulation results by the PSCAD/EMTDC show that the proposed protection can effectively identify DC line short-circuit faults,and is not disturbed by interferences,such as the fault resistance,noise and abnormal data. The proposed protection is suitable for flexible DC distribution networks with multi-type converters and distributed renewableenergy sources.