The invention relates to a welding repair technique for an inner hole of a back mounting edge of a back cover. The technique comprises the following steps: S1, blanking a rectangular material of an edge bar; S2, processing the hole wall of the inner hole; S3, welding the edge bar for one circle along the hole wall; S4, processing the hole wall of the welded inner hole; S, correcting the circle run-out and the coaxiality of the processed inner hole, and then finely turning the hole wall of the inner hole such that the aperture of the repaired inner hole is accordant with the actually needed aperture; and S6, finally implementing coal oil penetrant inspection. The technique adopts a welding tool, such as argon arc welding to weld the edge bar with a matched size onto the wall surface of the inner hole of the back mounting edge, so that the defects of severe abrasion and crackle on the inner wall surface of the inner hole are repaired, the hardness and the wear resistance of the inner wall surface are improved, and the heat deformation is low. And at the same time, the repairing pass percent of the wall surface of the inner hole can be guaranteed better, the repairing efficiency is improved, and the production cost is reduced.