Abstract: Low alloy cold die steel belongs to high carbon steel, so the quenching crack is easy to appear when it is hardened. The cold die with a large dimension、complicated structure and high precision will soon have to be scrapped because of there exists the quenching crack in it. How to repair the cold die with quenching crack is badly needed in industrial productions. The method of lapping repair for quenching crack inside the cold die steel has been studied in this paper in order to prevente the crack. The experimental research has been done. Firstly, the crack prevention has been executed around the tip of quenching crack inside the cold die of 9SiCr steel through pulse current discharge, the curvature of the crack tip will be increased after the crack prevention, so the crack can be prevented from extending. Secondly, the spark discharge is applied to the crack in surface with YG8 electrode, a reinforced layer which covers the crack can be formed, and it could be considered as a bridge in the tip of crack. After the lapping repair, the stress concentration can be caused in the die since there exists the similar area inside the reinforced layer. So the tip of crack under reinforced layer is treated with on the second pulse current discharge and the lapping repair for quenching crack inside cold die steel can be obtained.