The structural evolution of poly(butylene succinate) (PBS) during tensile deformation was investigated by in situ synchrotron X-ray scattering. Crystal transition during stretching was identified at 30-90 degrees C. An increase of long period was observed during the alpha-beta crystal transition, which was attributed to the increase of both amorphous layer thickness and crystalline layer thickness (lamellar thickness). The reversibility of crystal transition and correlation of lamellar thickening with crystal transition were confirmed by a "step-cycle" deformation measurement. The variation of the amorphous layer was partially recoverable, while the variation of lamellar thickness was nearly fully recoverable. The different repeating length in unit cell along the chain axis in different crystal forms resulted in the variation of the lamellar thickness. The different recoverability of structural parameters was interpreted by the different dynamics of the amorphous and crystalline phase.