There is little industrial experience and projects for semi-submersible platform with large volume condensate storage tanks. The hull structure design of condensate storage tanks were provided. Firstly, the column was designed with the double-wall voids (cofferdams ) around the condensate tanks and connected with flats with manholes for maintenance access. Secondly, the pressure head of condensate tank was increased by 10 m compared to the ballast tank after optimizing the reduction of 20 m. Thirdly, the bulkheads of condensate tank are non-watertight and continuous, but with the upper and lower 2 m height gaps for the flowing of condensate and gas. Fourth, the additional corrosion margin of 2 mm was added to the boundary of frequently ballast and de-ballast tanks in the nodes and columns. It is a successful practice for other similar design in the future.