Assessing the safety of amphibious aircraft hinges significantly on two key factors: wave-added resistance and motion stability during takeoff and landing on water surfaces. To tackle this, we employed the Reynolds-averaged Navier–Stokes (RANS) equations solved via the finite volume method. We utilized the volume fraction method to accurately capture the free surface and employed the overset grid technique to manage the relative motion between the aircraft and the liquid surface. Our approach involves establishing a numerical simulation scheme to investigate the water-planing motion of amphibious aircraft across varying wave heights, wavelengths, speeds, and center-of-gravity positions. The computational findings demonstrate a close match between calculated forces and aircraft motion compared to experimental values. Notably, we observed pronounced nonlinearity in wave-added resistance. Under high sea conditions, operating in a short-wavelength environment or with a rearward center-of-gravity position proves advantageous for reducing wave-added resistance. Conversely, poor longitudinal stability is evident during planing in long waves.