This article presents a hybrid algorithm for improving the accuracy of wavefront reconstruction of a defocused Shack-Hartmann wavefront sensor using the moment method. For a defocused Shack-Hartmann sensor, not only the shift of centroid for each microlens spot but also the second-order moment of each spot are extracted for calculating the local slopes and curvatures of the input wavefront. To improve the accuracy of the wavefront reconstruction, we employ these calculated slopes and curvatures to reconstructure the input wavefront instead of just using the calculated slopes for the conventional Shack-Hartmann sensor. The proposed method is verified by numerical simulations. It shows that the proposed method is useful for wavefront reconstruction with high accuracy. For example, the root mean square value of the residual wavefront error for reconstruciton of the peaks function is 0.0327λ using the proposed method, which is smaller than that, i.e., 0.0903λ, using the conventional method, indicating the proposed method can significantly improve the accuracy of the wavefront reconstruction.