Based on the long-term experiment in long-term cotton-cropping field, this paper analyzed the characteristics of soil organic carbon mineralization and the change patterns of soil organic carbon release under the conditions with and without straw returning. The results showed that straw returning increased soil total organic carbon (TOC) and mineralizable carbon (MC) contents and mineralization rate (MR) in 0 – 60 cm soil layer, and trended to increase with the increase of cropping year but to decease with the increase of soil depth. With the increase of continuous cropping years, soil organic carbon MC and cumulative mineralized emissions (CO₂-C emissions) showed an increasing tendency, however, mineralization intensity showed a decreasing tendency with straw returning, while showed opposite tendencies without straw returning. It demonstrates that straw returning promotes soil biological activity, compensates soil organic carbon but not enough to stabilize or increase carbon sequestration capacity of long-term continuous cotton-cropping field of Xinjiang Oasis.