The forward motions of the ultra-high-speed aerodynamic alleviation marine vehicle (AAMV) with or without steps under different sailing conditions are simulated by using the finite-volume-method (FVM) based STAR-CCM+ software, in order to explore the influence of the step on the hydrodynamic and aerodynamic characteristics of the ultra-high-speed AAMV. The calculated results are analyzed to show the mechanism of the step and its effects on the hydrodynamic and aerodynamic forces, ship’s attitude and wettingwetted area of the ultra-high-speed AAMV. It can be concluded that the step significantly reduce the resistance at high speed with a maximum resistance reduction of 33.7%. It also shows that the step mainly affects the aerodynamic alleviation rate at high speed where the ship width Froude number ( Fr) is larger than 4.04. At the maximum speed, the aerodynamic alleviation rate of the step model is increased by about 16.7%.