At present, the voltage source coverter-based high voltage direct current （VSC-HVDC） transmission technology is usually adopted to access large-capacity offshore wind power to the power grid. A symmetical monopole wiring scheme is adopted for the offshore DC project currently in operation. Although the symmetrical bipolar scheme has a higher initial investment, its high reliability can improve the power generation profit in the operation stage. Based on the scale of 2 GW offshore wind power VSC-HVDC transmission, this study compares the design of symmetrical monopole system and symmetrical bipolar system. Two schemes for the layout and structural design of offshore converter station platform are proposed, and the initial construction investments and full life cycle profits of the two schemes are calculated. The results show that the symmetrical monopole scheme has economic advantages in whole life cycle economy compared with the symmetrical bipolar scheme.