Abstract: Benefit from the refined design of the hull layout, the seaplane can efficiently take off and land on the water surface. In-depth understanding characteristics of the water take-off and taxiing is crucial for the development of aircraft. Two research methods, towing test and numerical simulation method, are used to explore the flow mechanism, and the hydrodynamic characteristics of the large-scale amphibious seaplane during taxiing are analyzed. In order to ensure that the hydrodynamic and aerodynamic forces in the towing test are similar at the same time, the force and moment are unloaded, meantime the rigid external force module is added to the calculation platform to simulate the test unloading. The results show that CFD technology can be used for the two-phase flow coupling six-degree-of-freedom motion of complex shape without any detrimental loss of accuracy, and the flow field and model dynamics in the test are reproduced by simulation, yielding that the resistance error is within 10% during the whole take-off process. Furthermore, for large amphibious seaplanes with landing gear, the strong splash from the fore-body hull is the root cause of the hump drag.