The invention discloses a method for restoring a crack of a blade of a hydraulic turbine. The method mainly comprises a preparation stage, a self-melting welding stage, a filling welding stage and an aftertreatment stage. At the preparation stage, the blade to be restored is cleaned and detected; at the self-melting welding stage, an inclined convergent laser beam with a negative defocusing amount is adopted for carrying out scanning in the extending direction of the crack, a V-shaped melting pool is formed, and molten metal liquid sinks to the bottom of the melting pool under the action of gravity, and is solidified to form a self-melting weld joint; at the filling welding stage, a material identical to a body of the blade is adopted as a welding wire for surface layer bead welding; at the aftertreatment stage, distressing tempering and blade surface finishing machining are carried out after welding is completed. In the restoring process, based on self-melting of the material of the body of the blade, the blade is filled with a few materials identical to the body of the blade, the material of the weld joint is identical to that of the blade, the material and the blade are combined well, a weld joint defect is not likely to be generated, and the combining strength of the weld joint is improved. In the self-welding welding and filling welding processes, molten metal in the melting pool is vibrated through ultrasonic waves generated by an ultrasonic generator on the back face of the blade to remove gas, and the defects of weld porosity and the like are reduced.