Floatover technology has been widely used in offshore installation, which has many substantial advantages compared with the traditional derrick barge. During the topside offloading of a twin-barge floatover installation, the transport barge is side by side moored between two floatover barges. In this paper, the twin-barge model with the connecting hawsers and pneumatic fenders is established. Coupled dynamic analysis is carried out to investigate the motions of the barges under wind, wave and current environments. Particular attention is paid to the effects on system responses with different frictional performance of fender, axial stiffness of the hawsers and environmental conditions. The research results can be used for optimizing the parameters of the system and reducing the risk of topside offloading.