Abstract: The damage of FPSO side structures subjected to a collision may lead to severe consequences such as oil leakage. Attention should be paid on the anti-collision capability of the FPSO side structure during the phase of preliminary structure design. The application of a simplified analytical method can significantly improve the efficiency of structure design in the preliminary design stage. In this paper, a simplified analytical method for the anti-collision capability of FPSO side structures is proposed, based on a series of closed-form solutions for individual structural members developed from their plastic mechanism analyses. By this method, the deformation and the resistance of the damaged structures, including outer plating, longitudinal girder, transverse web frame and inner plating, can be calculated when the collision scenario is defined. The method is verified by numerical simulation, in which three typical collision scenarios are defined and the FPSO side is struck by a ship with a bulbous bow in all scenarios. Thus the applicability of the simplified analytical method is developed for the FPSO side structure design.