FLNG is applied in deep offshore and marginal oil fields. Tandem offloading system of FLNG has great adaptability to the environment and higher safety, which is the development trend of floating LNG offloading system. Considering the coupling effects of wind, wave, current and mooring floating structure, the model test of tandem offloading system of FLNG and LNG carrier is carried out in this paper. The coupling motion characteristics of multi-floating body system in waves are studied in this test, and the relative motion characteristics of LNG transportation positions in tandem system under different combination of environmental factors and connection modes are analyzed. The results show that the double-hawser connection between FLNG and LNG carrier of the external turret mooring system is better than the single-hawser for stability of the system. The length design of FLNG cryogenic hose shall consider the maximum distance in the relative movement of translation positions in the combination of wind, wave and current in different directions, and the dynamic variation range of the rotation in the combination of wind and wave in the same direction shall be considered in design of the end of hose.