Abstract: Aiming at providing theoretical basis for soil carbon sequestration and sustainable utilization of black soil, we studied the effects of straw returning to field after continuous cropping maize(Zea mays L.) on aggregates and organic carbon content of black soil.We selected a typical black soil with 5-year continuous cropping maize, and analyzed soil aggregates, organic carbon, bulk density, and field water holding capacity under straw returning combined with nitrogen fertilization to explore the effects of continuous return of straw on soil physicochemical properties.The mechanical stability of soil aggregates was averagely with 30.2% of soil particle content within a diameter of 10 mm or greater sizes, and the content in 0-20 cm soil layer was with the highest value.The water stability of soil aggregates decreased gradually with the increase in soil depth.In terms of stability, nitrogen treatment was more effective than no nitrogen treatment; straw returning treatment was greater than straw non-returning treatment.The content with soil aggregate size of ≥0.25 mm was in an order of ST-OPT(Optimized fertilization with straw returning)>ST-NO(No nitrogen fertilizer with straw returning)>OPT(Optimized fertilization)>CK-NO(No straw and no nitrogen fertilizer).There was a significant linear correlation between soil bulk density and field water holding capacity(r=0.884).The organic carbon content in 20 cm soil layer was with the highest value, while that in 30-50 cm was not significant in different particle sizes.The organic carbon content with aggregate of 2-1 mm size was 35.1 g·kg^-1, 14.5% higher than other aggregates.Compared with CK-NO treatment, OPT, ST-OPT and ST-NO treatments averagely increased SOC content by 10.5%, 2.01%, and 5.50%, respectively.Straw returning combined with nitrogen fertilization was beneficial to the soil macro-aggregates formation and the organic carbon contents, and the contribution of organic carbon in soil macro-aggregates to total soil organic carbon increased significantly.