The invention discloses a converter fault protection method for a multi-converter direct-current transmission system, which comprises a collection link and a judgment and processing link, wherein thecollection link is used for collecting direct current flowing through a valve bank, upper and lower bridge arm current and converter valve and coupling transformer lead current, and all the current directions take the direction pointing to the converter valve as the positive direction; and the judgment and processing link is used for extracting and calculating grounding fault characteristics of the converter valve and the converter valve and coupling transformer lead according to the analog quantities collected by the collection link, judging whether a grounding fault occurs in the converter valve or the converter valve and coupling transformer lead area or not, and if it is confirmed that the grounding fault occurs in the converter valve or the converter valve and coupling transformer lead area, exiting the direct-current differential protection of the valve bank. The method can effectively solve the problem of identifying the grounding faults of the extra-high voltage flexible directcurrent converter valve and the grounding faults of the converter valve and coupling transformer lead area, effectively reduces the probability that all valve banks of the whole pole are locked due to the grounding faults of the valve banks, and guarantees the power transmission to the maximum extent.