The invention discloses a method and a system for acquiring the measure amount of a direct current bipolar line fault of a flexible direct current grid, which belongs to the technical field of power system safety and stability control. The method provided by the invention comprises the steps that the fault of a direct current bipolar line Li is determined; the measure amount of the direct currentbipolar line fault is determined when a converter Si_x is locked due to the direct current bipolar line fault; and when a converter station Si is locked due to the direct current bipolar line fault,the measure amount of the direct current bipolar line fault is determined; and when single pole locking and single station locking are not caused by the direct current bipolar line fault, the measureamount of the direct current bipolar line fault is determined. According to the invention, when a flexible direct current grid safety control system has a converter locking fault, the safety control system thereof can calculate the correct fault measure amount; and safe and stable operation of the flexible direct current grid can be effectively ensured.