For the weak target detection, the existing methods still have the problem of large detection error. In order to improve the accuracy of the centroid detection of the Shack-Hartmann wavefront sensor, an improved distance-power index centroid detection algorithm is proposed. The proposed algorithm is compared with several existing centroid algorithms under different conditions, the simulation results show that the centroid detection error of proposed algorithm is lower and more stable than that of other algorithms under the factors of different signal-to-noise ratios, different spot diameters and different pixels in sub-area.