As a key device of cylindrical FPSO, motion suppression structure plays an important role in reducing the sag and pitch motion of the platform. The connection structure between the extension cylinder and the reducing device is the key to ensure the structural design. In order to verify the rationality of the structural design scheme, the structural strength of the motion suppression structure under towing and working conditions is studied by MSC.Patran/Nastran software, and the appropriate connection structure is selected. According to the results of strength calculation, the optimization suggestions of key components such as watertight bulkhead and non-watertight bulkhead, strong frame and non-watertight bulkhead of reducing device and connecting structure are put forward. Combined with the analysis results and construction technology, the toggle plate connection structure is selected as the final design scheme.