The utility model discloses a half-open type offshore transformer station comprising an offshore platform. A main voltage transformer, a high-voltage power distribution device, a middle-voltage power distribution device, a low-voltage power distribution device, a station-used voltage transformer device and a diesel generator are fixed on the offshore platform. The main voltage transformer is arranged in a middle position of an outdoor space. The other devices are all arranged in a metal enclosed space. The main voltage transformer employs a low-voltage winding split type on-load voltage regulation voltage transformer. The two sides of the low-voltage winding split type on-load voltage regulation voltage transformer are respectively connected with a high-voltage power distribution device and a medium-voltage power distribution device. The medium-voltage power distribution device is connected to a low-voltage power distribution device, and is also connected to the station-used voltage transformer device. The beneficial effects of the half-open type offshore transformer station are that a half-open type structure is adopted, i.,e., the main voltage transformer is arranged outdoors and the other devices are all enclosed in a metal enclosed spatial structure, consideration can be given to demands of offshore platform electrical equipment anticorrosion and main transformer ventilation and heat radiation.