A two-year stationary field experiment under the crop rotation of wheat-corn was carried out in Shajiang black soil to study effects of incorporation of straws on soil nutrients and labile organic carbon. The experiment was designed to have five treatments, i.e. no fertilizer (CK), chemical fertilizer alone (F), chemical fertilizer + straw (FS), chemical fertilizer + straw + organic matter-decomposing inoculant (FSD), and chemical fertilizer 20% less than Treatment F in terms of P₂O₅ and K₂O + straw + organic matter-decomposing inoculant (F_4/5SD). Soil samples were collected in the plough layer of the field after the crops were harvest, for analysis of contents of nutrients, labile organic carbon and microbial biomass carbon. Results show that the compared with Treatment F, Treatment FS increased alkalystic N, available P, available K, labile organic carbon , ALC and CPMI by 13.0%, 4.6%, 10.7%, 12.0%, 11.1% and 30.6%, respectively, and Treatment FSD did alkalystic N, available P, available K, labile organic C, soluble organic C, A_LC and CPMI by 17.4%, 40.5%, 12.4%, 12.0%, 51.3%, 9.5%, 102.3%, respectively, when compared with F. Correlation analysis shows that CPMI was better related to total N, alkalystic N, available P, available K, microbial biomass C and liable organic C in the soil than total organic C. Quite obvious, incorporating crop straws into the field with organic matter-decomposing inoculant is conducive to increasing soil nutrients, labile fraction of organic carbon, A_LCand CPMI, that is to say, even if the application rate of P and K fertilizers is reduced by 20%, the soil-building effect of this practice will not decline significantly.