Abstract: The analysis and discrimination of DC faults is an important problem that needs to be solved in the flexible DC system. This paper derives a bus-side simplified circuit fault calculation method for MMC-MTDC and analyzes the fault characteristics of bus-side pole-to-ground fault and pole-to-pole short circuit fault. Based on the results above, a fault discrimination scheme for multi-terminated flexible DC transmission networks are designed. The discriminative scheme uses three modules for fault discrimination, and adopts the post-fault voltage dip peak and post-fault line current value as the fault characteristic quantity, and the whole discriminative scheme is not affected by other component parameters, fault location and other factors. The combination of Spearman correlation analysis and traditional electrical fault area discrimination accurately determines faults within and outside the system area, while solving the problem of misjudgment caused by interference of line parameters in fault area discrimination, and the simulation test verifies the feasibility of this protection scheme.