Abstract: The flow of a new unsmooth surface-dimple concave surface in air was simulated numerically and the drag reduction coefficients of both unsmooth surface and smooth surface with hemisphere of 0.4mm dius were presented. The result showed that this kind of unsmooth surface had a good drag reduction effect for flow velocity ranging from 4m/s to 48m/s. And it had the best reducing ability (7.2%)at a velocity of 24m/s. The theory of the drag reduction was finally analyzed.