In this paper, the DC-side fault detection and protection scheme of DC system are studied. The DC-side fault characteristics of DC system are analyzed. Then, a fault detection and localization scheme using the rate of change of current measured at the line side with the R-L parallel fault current limitation is proposed to improve the fault detection speed. A backup protection scheme for the fault isolation when the outlet breaker operates incorrectly is proposed for DC system which adopt DC breaker. A four-terminal DC grid simulation model is built based on thePSCAD/EMTDC to verify the effectiveness of the designed fault detection method and protection scheme.