Pump-jets have a relatively high propulsion efficiency at medium speed and in heavy-load conditions for wheeled amphibious vehicles. However, the geometry of amphibious vehicles is very special due to the installation requirements of the pump-jet, which results in an obvious resistance on the wheels. In order to reduce the resistance of the amphibious vehicle, the resistance characteristics of the wheels are studied. Regarding a pump-jet-propelled wheeled amphibious vehicle, its wheel resistance characteristics in a wide speed range are firstly analyzed based on experiments and numerical simulations. By comparing the resistance of the amphibious vehicle with and without wheels, it is found that the hydrodynamic effect of wheels can increase the total resistance of the amphibious vehicle by 14~28%. Then, the wheel hydrodynamic effect is divided into local effect and global effect. By analyzing the changes in resistance, pressure distribution and streamline, the influence and hydro-mechanism of each effect are explored in detail. It is found that the longitudinal convex and concave structures formed by the wheels and wheel wells have a large negative effect on the total resistance. According to the hydro-mechanism, two resistance improvement approaches are proposed, which includes increasing wheel retraction and installing flat plates on the wheel well bottom. Finally, the ultimate resistance improvement model can reduce resistance by no less than 10% and power by on less than 8% in design speed.