Abstract: The impacts of straw mulching and returning on the storage of soil dissolved organic carbon (DOC), particulate organic carbon (POC) and mineral associated organic carbon (MOC), and their proportions to the total organic carbon (TOC) were studied based on a field experiment. The results showed that compared to the treatment of wheat straw soilreturning (WR), the storage of TOC and MOC decreased by 4.1% and 9.7% respectively in 0-20 cm soil in the treatment with wheat straw mulching (WM), but the storage of DOC and POC increased by 207.7% and 11.9%, and TOC and POC increased significantly in 20-40 cm soil. Compared to the treatment with maize straw soilreturning (MR), the storage of TOC and MOC in the plough pan soil of the treatment with maize straw mulching (MM) increased by 13.6% and 14.6%, respectively. Compared to the WR-MR treatment, the storage of TOC and MOC in top soil (0-20 cm) significantly decreased by 8.5% and 10.3% respectively in WM-MM treatment. The storage of TOC and POC in top soil was significantly higher in the treatments with maize straw soilreturning or mulching than that with wheat straw. Compared to the treatment without straw (CK), the storage of TOC in top soil increased by 5.2% to 18.0% in the treatments with straw returning or mulching in the six modes (WM, WR, MM, MR, WM-MM,WR-MR)(P<0.05), but the storage of TOC in the plough pan soil decreased by 8.0% to 11.5% (P<0.05) except for the treatments of WM and MM. The storage of DOC and DOC/TOC ratio decreased significantly in top soil in the treatments with straw mulching or returning in six modes. The storage of POC and POC/TOC ratio in WM and WM-MM treatments, MOC and MOC/TOC ratio in WR treatment, increased significantly in top soil. In the other three treatments with straw mulching and returning (MM, MR, WR-MR), the storage of POC and MOC increased significantly in top soil. These results suggested that straw mulching had the potential to accumulate active organic carbon fraction in soil, straw soilreturning had the potential to accumulate stable organic carbon fraction. Considering organic carbon sequestration in cropland in the region of Guanzhong plain, maize straw mulching or soilreturning was better than wheat straw, and wheat straw and maize straw soilreturning (WR-MR) were better than wheat and maize straw mulching (WMMM).