The invention relates to a direct-current grid hierarchical control system and a design method thereof. The direct-current grid hierarchical control system comprises a direct-current grid overall coordinated control layer, a multi-convertor station coordinated control layer in regional direct-current sub-grids, and a voltage source converter station (VSC) body control layer which is connected withthe regional direct-current sub-grid coordinated control layer, wherein the multi-convertor station coordinated control layer is connected with the direct-current grid overall coordinated control layer; the direct-current grid overall coordinated control layer and the multi-convertor station coordinated control layer in the regional direct-current sub-grids adopt an active/standby control mode; and the control system also comprises a direct-current grid wide-area measurement system (WAMS) connected with the direct-current grid overall coordinated control layer and the multi-convertor stationcoordinated control layer in the regional direct-current sub-grids. According to the direct-current grid hierarchical control system and the design method thereof provided by the technical schemes ofthe invention, the converter station main body control layer, the sub-grid coordinated control layer and the overall grid control layer are adopted, so that the multi-level effective coordination andcooperation of the control functions of a direct-current grid can be realized. The control system has the advantages of clear structure and explicit functions, and can ensure the safe and stable operation of the direct-current grid.