The invention discloses a method and a system for obtaining fault measure quantity of a direct current neutral bus of a flexible direct current power grid, which belong to the technical field of safety stability control of electric power systems. The method includes the following steps: when the direct current neutral bus of a converter station fails, converters Si_x and Si_x' are blocked; systemunbalanced power [delta]P=P+P caused by the direct current neutral bus is obtained; the fault measure quantity of the direct current neutral bus is obtained; and allocation principlesof the fault measure quantity of the direct current neutral bus in two sending end stations are determined. The method and the system ensure that a safety control system of the flexible direct currentpower grid safety control system can calculate to obtain correct fault measure quantity when a blocking fault of the occurs, and can effectively ensure safe and stable operation of the flexible direct current power grid.