The invention discloses a flash welder repair method, and belongs to the technical field of equipment repair. The flash welder repair method comprises the following steps: (1) upper and lower bases are decomposed; (2) equal-height iron blocks are manufactured; (3) the bottom surface of a base baseplate of a flash welder is used as a reference surface for metering detection of the mounting surfacehorizontal error and height of a wear resisting plate of the baseplate; (4) a plane after polishing of the wear resisting plate is used as a reference surface for polishing the bottom surface of the wear resisting plate to guarantee the same thickness; and the height error and the horizontal error of the plane after installation of the wear resisting plate are controlled within 0.02 mm; (5) the equal-height iron blocks machined in the step (2) are fixedly placed on a gantry milling machine worktable; and (6) a lower base is lifted on the equal-height iron blocks of the gantry milling machine worktable for metering detection of the mounting surface height size, horizontal error and parallel error of upper and lower base polar electric blocks; the milling and the manual grinding are performed after welding cooling; and then, the polar electric blocks are installed. The flash welder repair method can quickly and effectively improve the repair efficiency, and prevents the problem of welderprecision reduction.