Abstract: In order to deal with the defects of cast steel cracks in the precision machining or finished product stage of large high-precision gearbox welding boxes, and to avoid affecting delivery progress or causing significant economic losses, a type of small current multi-layer multi pass welding, pointed hammer impact stress release, and vibration stress relief repair method is proposed in the article, focusing on demonstrating the repair method from multiple dimensions such as ultrasonic testing, penetration inspection, welding process evaluation, deformation detection, hardness detection and stress detection. The ultrasonic testing and penetration inspection of the repaired gearbox welding boxes after the welding process evaluation are qualified; the welding boxes have not undergone deformation, and hardness and stress testing results are qualified. Through multi-dimensional verification such as deformation detection and stress detection, it is shown that this method can effectively control deformation and residual stress, which is reasonable and feasible. The analysis and repair methods have important reference value for treatment of the similar defects.