Deformation-induced crystallization of living polymer Sulfur was studied with in situ wide-angle X-ray scattering, where chain scission plays a critical role. The onset of crystallization always occurs at the minimum stress point after the yield point, though different drawing rates were applied. With large drawing rates, deformation effect dictates the chain scission and linear chain-ring transition, which leads to the formation of linear chain fibrous phase, while only cyclooctasulfur crystals form at small drawing rates where the thermal effect is mainly responsible for the chain-ring transition. The scission of linear chains not only generates the building units for crystallization but also releases chains from entanglement and consequently enhances their mobility and crystallization rate. A critical point is found at an intermediate drawing rate where no crystallization occurs before the complete breakage of the samples. With the large or small drawing rates, the crystallization rate is faster than rates of chain scission induced by deformation or the thermal effect; crystallization Occurs before sample breaking, where fibrous phase and cyclosulfur crystals act as cross-link and filler, respectively. With the critical drawing rate, the nucleation rate of crystals is slower than that of chain scission, and the sample breaks before the onset of crystallization.