Submarine sand waves have important influences on the construction and safety operation of ocean engineering. The tidal current is one of the main causes for formation of submarine sand waves. Based on the dimensional analysis, this study conducted the flume experiments to study the formation and development of submarine sand waves under the tidal current and unidirectional flows. By analyzing the seabed morphology data, this study quantitatively described the characteristic scale and evolution process, and discussed the effects of the speed and cycling period of the tidal current, the water depth and the combination of tidal current and unidirectional flow on the characteristic geometry of sand waves. The experiment results showed that the seabed topography produced by the tidal current is composed of large-scale sand waves and small-scale sand ripples, in which the former topography is dominant to shape the form of the seabed. Beginning from a flat seabed, the height and length of sand waves gradually increase and the growth rate decreases under the action of currents, and it reaches a dynamic balance finally. Both the characteristic wave height and characteristic wavelength of sand waves increase with the increase of flow velocity and water depth. They also increase with the increasing reciprocating flow period, finally tend to close to the condition of unidirectional flows. Furthermore, this study analyzed the topography of the small-scale sand ripples, and indicated the rule of characteristic scale of sand ripples under different currents.