The invention relates to a water cooling control system for a direct-current transmission converter valve and an alternating-current dual-power switching device and belongs to the technical field of direct-current transmission. Two three-phase power detecting elements (KVM1 and KVM2) are arranged on an alternating-current dual-power bus. The states of the alternating-current power detecting elements (KVM1 and KVM2) on the bus and the state of a power detecting element on an alternating-current power inlet line in an input state are detected, the voltage of the alternating-current bus is mainly detected, the voltage of the inlet line is secondarily detected, and accordingly switching control to the dual powers can be achieved. The alternating-current dual-power switching device is simple in structure, can effectively avoid accidents caused by switching powers by detecting the inlet line power as the basis and improves the stability of power systems.