Abstract: Using a method of free energy minimization,the magnetization properties of the ferromagnetic monolayer and ferromagnetic（FM）∕antiferromagnetic（AFM） bilayer under the stress field have been investigated.And then the relation between the magnetoresistance（MR） of the Spin-Valve structure and the applied stress field was investigated.Numerical calculation shows that under the stress field,the magnetization properties of the FM monolayer is obviously different from that of FM ∕AFM bilayer due to that the AFM layer coupled would obviously block the magnetization of FM layer.This phenomenon results to MR of the Spin-Valve structure to become obvious.Specially when the direction of stress field perpendicular to the easy axis,the magnetization direction would change from the easy axis to the stress direction at that moment at the stress field equal H_λ=2（K₁+K_up）/3M.Based on these investigations,the perfect mechanical sensor using the magnetoresistive effect induced by the stress field in nano-scale is suggested to be devised experimentally.