Abstract: The large underground drainage pump station has a large installed capacity, high equipment heat generation, and poor heat dissipation conditions. In order to prevent the air temperature inside the pump station from exceeding the limit, the water pump unit is equipped with a water-cooled electric motor, and an external water cooling system is used to cool the electric motor. The heat generated during the operation of the electric motor is discharged outside the pump station. This article takes engineering as an example, calculates the required heat transfer capacity and cooling water volume of the cooling system, and proposes two schemes: open direct discharge and secondary heat exchange. After comparing the technical and economic schemes, it is determined to adopt the secondary heat exchange cooling system scheme. Based on the determined technical scheme and design principles, the author calculated and selected equipment for cooling system heat exchange, pressurization, filtration, circulation, constant pressure water replenishment, and control．