Abstract: When a short-circuit fault occurs in a DC line, the sub-module capacitor is the main contribution unit for the short-circuit current before the blocking of the converter. Its extremely fast discharge speed poses a challenge to the safe and stable operation of DC grid. It is thus urgent to study the calculation method of the short-circuit current in DC grid. Firstly, the trapezoidal integration method is used to discretize the dynamic components in the established DC grid equivalent model. Then, the improved node method is used to construct the network equation, and the short-circuit current of the faulty branch is obtained through iteration. Furthermore, a new method is proposed to calculate the short-circuit current of DC grid based on adjoint network. A four-terminal real bipolar toroidal DC grid model is built in PSCAD/EMTDC software. According to the simulation results of different types of faults in DC lines, the proposed calculation method is compared with the typical state space method in terms of calculation accuracy and calculation efficiency. The error sources of the two methods are analyzed, and the effectiveness of the proposed algorithm is verified.