【Objective】The purpose of this study was to determine the amount of fertilizer that could be replaced by straw returning under the condition that crop yield and soil nutrients were not lost, and to reveal the microbial mechanism that promoted the efficient utilization of straw nutrients, so as to provide a basis for promoting the reduction of fertilizer application.【Method】A field experiment was set up in the fluvo-aquic soil area of the Huang-Huai-Hai Plain to study the effects of straw returning combined with different proportions of nitrogen and phosphorus reduction on soil nutrients. Also, the effects of these amendments on crop yields, straw nutrient release, and soil microorganisms were studied to clarify the nutrient components of chemical fertilizers that can be replaced by straw returning without loss of crop yields and soil nutrients. Importantly, the microbial mechanism that promotes efficient utilization of straw nutrients and provides a basis for the implementation of chemical fertilizer reduction action was explored.【Result】The results showed that compared with conventional fertilization, a 30% reduction of nitrogen or 50% reduction of phosphorus had no significant effect on crop yield and soil nutrient content. The straw degradation rate reached 43.33%-53.11% in the first season while the reduction of 30% nitrogen or 50% phosphorus could increase it by 12.40%, and the degradation rate reached 63.41%-75.62% after two years. Nitrogen reduction by 100% significantly reduced the abundance, species richness and diversity of bacterial fungi, while phosphorus reduction had little effect. Nitrogen and phosphorus reductions by 30% and 50%, respectively, mainly increased the relative abundance of Gemmatimonadetes longimicrobiaceae and Proteobacteria nitrosomonadaceae in bacteria, increased the relative abundance of Chrytridiomycota GS13 class in fungi, and decreased the relative abundance of Ascomycota sordariomycetes and Mortierellomycota mortierellomycetes. Redundancy analysis showed that the main environmental factors affecting bacteria and fungi were soil organic carbon (SOC) and total nitrogen (TN). 【Conclusion】In conclusion, straw returning combined with nitrogen reduction by 30% or phosphorus reduction by 50% has the potential to maintain fertilizer use efficiency and stable yield in the medium and high yield fields of fluvo-aquic soil.