Based on long-term experiment of Black soil in Gongzhuling, ¹³C labeled corn straw was incorporated to the field and incubated in-situ. The turnover of straw C in soil and its contribution to total SOC in different fertilization treatments with mulching were investigated, in order to provide a reference for soil fertility improvement and C sequestration in the Black soil region. The results showed that after straw returning to soil under no-mulching, the δ¹³C values of SOC was significantly higher (P<0.05) in the treatments of no fertilizer (CK) and chemical fertilizer (NPK) than that in the treatment of combination of organic manure (MNPK) and chemical fertilizer. The δ¹³C values of SOC after straw returning to soil under mulching ranged from -18.27‰ to -17.19‰ and were not significant different (P>0.05) among different fertilization treatments on the 360^th day. Content of straw C in SOC (¹³C-SOC) was significantly higher (P<0.05) under mulching than that under no-mulching. Especially, the content of ¹³C-SOC under mulching treatment was 1~3 times that under no-mulching treatments on the 60^th day, which indicated the soil moisture and thermal conditions under mulching promoted the accumulation of straw C in soil. The average contribution percentage of straw C to SOC in the treatments of CK, NPK, and MNPK under no-mulching was 1.28%, 1.32%, and 0.46%, and was 0.81%, 1.51% and 0.97% in those treatments under mulching, respectively. The results implicated that the supply of chemical nutrients of nitrogen, phosphorus and potassium promoted the accumulation of straw C in soil, which played a positive feedback for soil C sequestration.