Abstract: Multi-terminal flexible DC distribution network has small short-circuit damping and low inertia, and the fault development presents the characteristics of strong nonlinearity and stage due to the existance of a large number of power electronic devices in the system. Conventional short-circuit calculation methods concern fault characteristics of "points" and "lines", making it difficult to consider the network-level characteristics. Therefore, this paper focuses on the whole process of short-circuit fault from capacitor discharge to AC-side feed current, and introduces the theory of DC fault ports. On this basis, the fault network is simplified by using high-frequency equivalent characteristics, and then the approximate solution of the fault current in the capacitor discharge stage is obtained by the Laplace inverse transformation. Subsequently, the characteristic quantity of the whole network is obtained by fault-port impedance. In the steady-state AC feed stage, the converter port transfer matrix is established, the series-connected nodes in the network are eliminated after commutation overlap correction, and then the steady-state short-circuit calculation method suitable for multi-terminal flexible DC power grids is obtained. Finally, a simulation model is built based on PSCAD/EMTDC platform, which verifies the accuracy of the proposed short circuit calculation method under different fault locations and fault resistances.