In order to study the hydrodynamic performance of a segmented-track amphibious vehicle, and realize resistance reduction to increase speed, stern flaps were applied to the transom stern. Model towed tests and numerical simulations were carried out and both the results agreed well with each other. The longitudinal position of the center of gravity, the length and angle of the stern flap were studied and the resistance components were analyzed. Research results show that with the longitudinal position of center of gravity between 540～560 mm, the vehicle suffered least resistance. At the velocity between 3～5 m/s, the stern flap with a length of 156 mm and an included angle of 10° with the horizontal plane has the most obvious drag reduction effect. Compared with the resistance of original naked vehicle body, the resistance reduction rate is 34.3%. The installation of the stern flap can increase the hollow area at the rear of the vehicle, which is equivalent to increasing the length of waterline, thus increasing the length-to-width ratio. This research method shows that the resistance reduction and speed increase of amphibious vehicle can be effectively realized by properly adjusting the center of gravity and optimizing the parameters of wave plate.