The residual stress of the iPP surface layer in Al/iPP/Al under the influence of microwave irradiation was investigated by thin film (TF)-X-ray diffraction (XRD). Depending on the irradiation time, we calculated the macro residual stress, micro stress, and lattice static distortion stress. The results show that the macroscopic residual tensile stress of irradiated iPP samples dropped from about 12 MPa to 4 MPa. D-(300) (the p crystal phase) becomes larger from about 4 to 10 nm as the irradiation time increased, and the beta-form iPP becomes more perfect. However, for the alpha-form phase, D-(110) remains almost stable. Moreover, the microscopic distortion coefficient epsilon((300)) that decreases from approximately 0.03 to 0.018, becomes smaller than epsilon((110)) parallel to the irradiation time, so the microscopic stress of the p-crystal is decreased. In addition, the lattice static distortion energy of the alpha-form greatly increases from 2 to 6 MPa, but the lattice static distortion energy of the beta-crystals remains constant at about 1.5 MPa and is much smaller than that of the beta-crystals at the same irradiation time. These calculated results are in good agreement with that of the crystallinity and order parameter of the beta-crystals of the TF-XRD. The lattice distortion energy is a major portion of the plastic deformation, therefore, it suggests that the lattice static distortion energy is the main cause of alpha --> beta crystalline transformation. (C) 2004 Wiley Periodicals, Inc.