Currently, bionic non-smooth surface drag reduction technology with significant economic value and military value is still imperfect. Generally, dimple structure, flow velocity, fluid medium and other factors are related to the dimple surface drag reduction. In order to further analyze the pit surface drag reduction, the numerical simulation was carried on the flowing of dimple non-smooth surface with different spacing in air. The results show that this kind of unsmooth surface with dimples (r = 0.5s, h = 0.25mm, a = 5mm) has a good local optimum drag reduction effect on flow velocity ranging from 6m/s to 15m/s, and it has the best reducing ability (25.927%) at the velocity of 6m/s. Finally, the theory of the drag reduction and the impact of the dimples drag reduction factors (different spacing) were analyzed. Interval length relative to the concave surface size has an appropriate value.