Abstract: The crystal transformation process of isotactic polypropylene (iPP) sheet during the annealing solid?state stretching process was studied. The crystalline characteristics of the resulting iPP sheet were detected by X-ray diffraction and then the relative content of β-form crystals was calculated quantitatively. Furthermore, two-dimensional small-angle X-ray scattering (2D-SAXS) was adopted to monitor the α-β crystalline transformation process. In addition, the melting properties of iPP sheet were characterized by differential scanning calorimetry. The results indicated that the iPP sheet underwent a crystal transformation during the stretching process, resulting in the presence of a diffraction peak at 16.1 ° for the (300) reflection of the β-form cylindrites, and the oriented cylindrical structure could be observed from the 2D-SAXS patterns. A relatively high content of β-form crystals was produced under the stretching condition at 110 °C, and the highest content reached 6.75 %. The mechanical results showed that the notched impact toughness of iPP sheet was improved significantly, whereas the tensile strength increased slightly. In addition, it was found that the cylindrical structure was not damaged when the solid-state stretched iPP was annealed below 110 °C. However, after the annealing temperature exceeded 110 °C, the cylindrical structure was destroyed and the spherulite structure was formed again.