Coupled dynamic analysis of the Deep Draft Multi-Spar (DDMS) platform and the mooring system under the action of waves and current is carried out in the time domain.Using a geometrically nonlinear finite element method,the mooring-line dynamics is simulated based on the total Lagrangian formulation.Wave groups are obtained by the JONSWAP spectrum and an empirical wave envelope spectrum involving two envelope-based factors Group Height Factor (GFH) and Group Length Factor (GLF).The results show that the wave groups have a significant effect on the motion responses of the platform and the mooring line tensions.