The invention provides a method for repairing an underground diaphragm wall after jamming of a hydraulic grab. The method comprises the following steps of determining the position and the depth of the jammed hydraulic grab through ultrasonic detection; measuring the offset of the jammed hydraulic grab by using an automatic skew adjustment device of the hydraulic grab; making a planar projection skeleton map after the hydraulic grab is jammed; determining parameters of a new bent underground diaphragm wall; and constructing the bent underground diaphragm wall. The method is a construction method in which the new bent underground diaphragm wall is used, offset conditions of the jammed hydraulic grab are considered, and the method conforms to actual engineering. Water is stopped by steel sheet piles, the strength is enough, and the problem that water cannot be stopped during construction of the underground diaphragm wall is solved. A round tube water stopping device is arranged at a junction of the new wall and the old wall, and the problem that water leaks due to concrete shrinkage is solved effectively. The method is simple and practical, and is convenient to popularize; underground continuous wall repairing practices are enriched; and the application value is quite high.