Abstract: The fault current level of a DC grid determines the cost of current limiting devices and the lifetime of converter components. The fault current can be effectively reduced by optimizing the DC grid topology. However, the existing fault current level evaluation index of DC grid topology is inaccurate and fails to represent the comprehensive fault current level under different operation modes. In view of this, an optimal design method for DC grid topology is proposed to restrain fault currents under different operation modes. First, the calculation method for short-circuit fault current in DC grids is presented. Then, a general representation of the grid topology is established based on graph theory, upon which the evaluation indices for fault current levels under normal operation mode and N-1 operation modes are proposed. Finally, an optimization method for DC grid topology is proposed considering the fault current levels under different operation modes. The effectiveness of our method is validated through the simulation using a six-terminal DC grid in PSCAD/EMTDC.