A new kind of adaptive optics (AO) system, in which several low spatial frequency deformable mirrors (DMs) with optical conjugation relationship are combined to correct high-order aberrations, is proposed. The phase compensation principle and the control method of the combinational AO system are introduced. The numerical simulations for the AO system with two 60-element DMs are presented. The results indicate that the combinational DM in the AO system can correct different aberrations effectively as one single DM with more actuators, and there is no change of control method. This technique can be applied to a large telescope AO system to improve the spatial compensation capability for wavefront by using current DM.