Abstract: A control sy stem of underwater high-pressure local dry automatic welding testing apparatus was developed.The testing apparatus is driven by hydraulic power, and can be applied in MIG process within the local dry cavity of the drainer.The system is mainly made up with Siemens PLC, pressure sensor, travel switch, and underwater swing center sensor.It is divided into three subsystems, the welding environment control subsystem, the control subsystem of automatic welding equipment driven by hydraulic power and the underwater monitor subsystem, which can realize underwater high-pressure local dry automatic remote control welding.Experiment results indicate that the system can work stably, and qualified joint can be obtained.The research work has established the foundation for underwater welding repair of unclear power station.