Abstract: Al thin films with the thickness of 300 nm were deposited on polyimide（PI） substrate by direct current sputtering.All films were treated by rapid thermal annealing（RTA） with different temperatures and time.The films’ microstructure and stress were studied by X-ray diffraction,scanning electron microscope and testing curvature.The thin film stress can be relaxed and changed from compressive stress to tensile stress by using RTA.