A multilevel wavefront correction technique is proposed to improve the effective correction bandwidth of a high-resolution adaptive optics system based on stochastic parallel gradient descent (SPGD) algorithm. At every level of wavefront correction based on SPGD, the control elements of the high-resolution wavefront corrector are subdivided into many clusters according to their locations. The control elements in each cluster are driven by the same control voltage which is treated as a control variable in SPGD algorithm. The higher the correction level is, the bigger the number of independent control variables is. The multilevel SPGD adaptive optics system corrects the distorted wavefront in the sequence from low level to high level. The numerical model of a 3-level SPGD adaptive optics system with a pixelated piston-type wavefront corrector having 16×16 control elements was built, and the simulation correction experiments for a certain stochastic phase screen introduced by atmospheric turbulence were performed on the system. The numerical simulation results demonstrate that the convergence rate of multilevel SPGD wavefront correction is increased by 23% than that of conventional SPGD wavefront correction. It indicates that the multilevel wavefront correction technique can indeed improve the effective correction bandwidth of adaptive optics system based on SPGD algorithm.