Quenching is the technology that a metal work piece heated to propriety temperature for a while is being put into quenching medium suddenly. Quenching can improve the rigidity and abrasion resistance of metal. Making use of PLC to control quenching process, the quenching has simple technology, cheap price, stable function and convenient operation. This quenching system constitutes heating system, quenching liquid cycle system, hydraulic pressure system and electric control system. The quenching machine control system introduced in this thesis has three control modes, Manual, Auto and Try-piece designed utilized S7-PLC. This system can rise and fall worktable, clamp and relax work piece, sway forward and backwards, unload-work piece control high degree by approach-switch, produce many kinds of auto-spring plate, meet the requirement of auto-spring plate nowadays. It is presented in this thesis detailed, control-demand, element list for electric control, I/O distribute list, control LAD and improved measure for system in the end.