Field experiment was designed to study changes of the carbon content of each component in soil humus,soil enzyme activity and their correlation when the maize straw was returned to the black soil at different depth treatments(0~15,15~30 and 0~30 cm).The results showed that soil organic carbon contents increased by 9.5%,9.9%,10.7% respectively than the original level of soil when the straw returned at depths 0~15，15~30，0~30 cm.Compared with the 0~15 cm,straw returned at depth 15~30 cm was helpful to the accumulation of soil organic carbon.Soil organic carbon content without strawreturning decreased by 5.8% than original level of soil.The each component of soil organic carbon and soil invertase activity was significantly(or very significantly)correlated.Soil humin carbon content and soil catalase activity was significantly correlated,and soil fulvic acid carbon content and urease activity were significantly correlated.