The invention discloses a semi-submersible platform building combining method. The method comprises the steps of building buoys, columns, a deck case, a living module and a cabin module. The buoys, the columns and the cross supports are combined to form a lower ship body; putting the living module on the deck case; combing the deck case with the living module with the lower ship body into a main ship body; combining the cabin module with the main ship body to form the semi-submersible platform. By the aid of the method, the requirement for semi-submersible platform building sites is reduced, the batch production of the semi-submersible platform can be achieved, and the building cost is reduced greatly.