In order to explore the effects of straw-returning depth on aggregate composition and organic carbon distribution in aggregates and soil, brown soil in Liaoning was used for a field micro-area experiment with crushed corn straw returning, in which 5 treatments were set up:CK (no straw returning) and four straw-returning depths of 0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm. Corn was planted and soil was taken in 2 years after straw-returning. Wet sieve method was used to obtain soil aggregates of 3 particle sizes:> 2 mm, 2-0.25 mm and <0.25 mm, and organic carbon contents in soil and aggregates was determined. The results showed that:1) The stability of aggregates and the content of large aggregates (>2 mm) were increased significantly after straw-returning to different soil depths (P<0.05). Returning straw to 0-10 cm and 30-40 cm increased the content of >0.25 mm aggxegates greatly, indicating the better improvement on soil structure; 2) Organic carbon content was reduced after straw-returning to 0-10 cm, 10-20 cm and 20-30 cm at one time two years later, and organic carbon content was significantly improved after straw-returning to 30-40 cm (P<0.05); 3) The input of straw promoted soil agglomeration process. Straw-returning to different depths had different impact on the distribution of aggregate organic carbon, but they all increased the content of organic carbon in large aggregates. The above results show that straw-returning improves soil structure and promotes the conversion of organic carbon from small aggregates to large aggregates, straw-returning to 30-40 cm has a more obvious promotion effect on soil agglomeration process and increases significantly soil organic carbon, thus, 30-40 cm is the more reasonable depth for straw returning.