Integrated design technology of external cooling system of voltage source converter (VSC) valve and water-cooled transformer is suitable for the design of key equipment external cooling systems such as converter valve and water-cooled transformer. This paper proposes a optimal design scheme for VSC valve and transformer external cooling system, which shares one water spray pool and one spray water treatment system, and also gives spray water yield analysis and calculation based on one stage and two stage of first level reverse osmosis system. This scheme can save water and reduce pollution, and is convenient for the converter station maintenance and management. It can be widely used in the equipment cooling system design of HVDC converter station on land and offshore wind power HVDC station.