【Objective】Organo-mineral complex is a kind of substance with soil organic colloidscomplexed with mineral colloids through surface molecular condensation, cation bridging and hydrogen bonding, which plays crucial role instabilization and accumulation of soil organic matter (SOM). Organo-mineral complexes are formed through interactions between organic matter (OM), mineral cations, metal oxides and soil clay minerals. Based on a long-term (10a) stationary experiment of straw returning to the field, this paper explores mechanism of straw returning affecting stability and accumulation of OM within organo-mineral complexes in typical Shajiang black soil, and systematically analyze distribution characteristics of OM content and mechanisms of OM complexing with metal cations and oxides typical in the soil, in an attempt to find out the key mechanism that constrains organic matter accumulation in Shajiang black soil.【Method】The long-term field experiment, which has been carried on since 2007, is designed to have five treatments, i.e. WMS+F (application of mineral NPK plusreturning of both wheat and maize straws), WS+F (application of mineral NPK plus returning of wheat straw only), MS+F (application of mineral NPK plus returning of maize stalks only), F (application of mineral NPK only) and CK (no-fertilization). 【Result】Results show that OM within the organo-mineral complexes existed mainly in the form of Fe/Al-bound organic matter (Fe/Al-OM) and tightly combined organic matter (TCOM), and both of them added up to 88.70% of the total organic matter (TOM). In terms of contents of the three forms of organic matters (Fe/Al-OM, TCOM and TOM), the five treatments followed an order of WS+F≈ WMS+F≈ MS+F>F>CK. Fe/Al-OM, TCOM and TOM was significantly and positively related to soil short-range ordered and organo-bound Fe/Al oxides, and negatively to amorphous Fe/Al oxides in content. 【Conclusion】Straw returning remarkably promotes the accumulation of SOM, which is affected by Fe/Al-OM. The slow formation of amorphous Fe/Al oxides brings about deficiency in content, thus restricting further accumulation of SOM. Although accumulation of Ca and Mg is one of the typical properties in Shajiang black soil, it has little impact on formation of OM in soil organo-mineral complexes because they are easily leached out. What’s more, the contribution of TCOM to TOM is significantly higher than that of Fe/Al-OM, of which relevant mechanism deserves further study.