Converter valve is a bridge arm of three-phase bridge converter to realize conversion current and basic equipment unit of a converter to realize the conversion between AC and DC. Its safe running plays a core role in the overall DC transmission. A safe and reliable closed loop water cooling system can precisely control the temperature, flow, and quality of cooling water, control and protect system and communication, maintain normal function of converter valve, a core part in HVDC system, and serve as the foundation of the stable running of HVDC system.