Abstract: An unsteady numerical simulation of a turbulent water flow field on a superhydrophobic surface shows the development of the gas membranes process on the hydrophobic surface, and the resistance reduction basic rule is summed up when the flow changes are stable. In the simulation, the unsteady Reynolds averaged model is used, the VOF multiphase flow model is used for the gasliquid two phase flow, and a hydrophobic surface microstructure grid with local encryption technology is adopted. The results show that the gas in the microstructure of hydrophobic surface changes continuously, a stable gas vortex forms at last in the upper part of each groove; the drag reduction rate of the hydrophobic surface first increases and then decreases with the flow rate increase; it also increases with the free shear ratio increase, but it is not significantly affected by the groove depth.