In order to restrict the deformable mirror to form the tip/tilt and piston aberration in close-loop adaptive optics(AO) system,the dynamic characteristic and the correction error of the system using least square algorithm by adding limitative aberration vector are analyzed, and the simulation result shows that the algorithm not only can not restrict the limitative aberration vector exactly，but also degrade the correction performance. Project-constraint algorithm to restrict the deformable mirror to form tip/tilt and piston aberration via aberration decouple and imposing limitative vector on control voltage is proposed. Simulation correction result for first 36-order aberration indicates only 0.02 pixels offset of far field is generated by deformable mirror via project-constraint algorithm, while 9.3 pixels offset using least square algorithm by adding limitative aberration vector, and higher Strehl ratio is achieved via project-constraint algorithm when correct for first 36-order Zernik mode aberration. The result shows that project-constraint algorithm can restrict effectively,and have better correction performance.