Biochar can improve soil fertility and reduce greenhouse gas emission, but its effect on soil organic carbon (SOC) mineralization is controversial. In this study, we used gray desert soil of Xinjiang as a case study and cotton stalk-char (BC) produced using cotton straw at 300℃ and 600℃ was used as a test material. Different proportions of BC were added to dry soil 0 (0BC), 0.1% (0.1%BC), 0.5% (0.5%BC), 1.0% (1.0%BC), 2.0% (2.0%BC), 100.0% (100%BC) (w/w), and then incubated at 25℃ under 75% saturated soil moisture condition for 100 d. The effects of BC on the SOC mineralization were evaluated. The results showed the following. 1) The BC with high temperature carbonization had smoother surface with neatly-arranged porous structure, the porosity and specific surface area increased, and the aromatization degree was enhanced. 2) A significant power function correlation was observed between the SOC mineralization rates over time (P < 0.05). Compared with the biochar produced at 600℃, the accumulated amount of mineralization and cumulative mineralization rate of SOC with biochar produced at 300℃ increased by 318% and 87.06% respectively. High temperature carbonization inhibits SOC mineralization. Except in the 0.1% BC treatment, the cumulative quantity of SOC mineralization with the addition of biochar produced at 300℃ increased by 3.05%-35.28% compared with that of the control treatments, and it increased with the content of BC added. On the contrary, the amount of accumulative SOC mineralization decreased by 6.11%-10.79% with the biochar produced at 600℃. 3) The positive priming effect during the early stage of incubation (0-20 d) on the native organic carbon mineralization of gray desert soil (except the 0.1% BC treatment). Whereas, the biochar produced at 300℃ showed negative priming effects during the late stage of incubation. However, it showed a negative priming effect throughout the incubation period. A similar trend was observed for the treatments with biochar produced at 600℃, and the positive priming effect was negligible during the early stage of incubation (0-5 d). Therefore, the biochar produced from cotton shell at low temperatures can enhance the SOC mineralization, whereas BC with high temperature carbonization inhibits SOC mineralization. The SOC accumulation can be increased with the addition of BC to soil due to negative priming effects.