Abstract: Fault current calculation is the basis for equipment selection, parameter designing and protection setting of DC power grids. However, it is difficult for present methods of fault current analysis based on detailed electromagnetic transient simulation to apply to large-scale DC power grids. For this reason, a general calculation method is studied to be applied to fault currents of a DC grid with different topologies. First, the coupling mechanism of the fault currents in each loop after the double-terminal DC system failure is analyzed. A fault circuit decoupling method is proposed based on the loop inductance parameter index; based on the principle of energy conservation, the series-parallel equivalent of network components and the unlooping of the multi-terminal ring network are put forward. In the method, the multi-terminal network is de-looped into an open-loop network, which is uniformly equivalent to a double-terminal fault network; and finally, the fault current decoupling method is used to obtain the time-domain analytical formula of the fault currents. A simulation system with a variety of topologies is built on the RT-lab simulation platform to verify the proposed method. The results show that the proposed method has good applicability to DC grids with different topologies, and is compatible with detailed electromagnetic transients. Compared with the detailed electromagnetic transient simulation, the proposed method has got basically less than 5% of the calculated current error.