The numerical simulation analysis is performed on wet store and temporary hanging-off operation of flexible risers in mooring system by finite element software. The mechanical characteristics of the mooring system components and flexible risers, the effects of wave and current as well as the vessel motion response are considered. The simulation is performed in the condition of 100-year-return typhoon sea state. The applicability of wet store and temporary hanging method is proved by the simulation analysis. The hanging off tension of the flexible riser is acquired through the simulation analysis and the length and strength of hanging-off rigging are confirmed. The guidance for offshore operation of mooring system replacement and reference for similar engineering projects can be provided by the simulation analysis method and results.