【Objective】 Plant residue is an important source of soil organic matter. Returning Straw to the field is an effective way to develop sustainable organic agriculture. In this paper, characteristics of the decomposition of plant straws, soil microbial functional diversity and their relationship was studied in an attempt to lay down a scientific basis for research on transformation of organic carbon in soil and rational exploitation of land resources. 【Method】The mesh bag method was used to explore how fresh plant straws decompose in farmland soil and the biolog plate technology was adopted to determine changes in soil microbial community relative to type of the plant straw incorporated.【Result】Results show that with decomposition going on, residue rate of fresh plant straws did not vary much. Corn straw decomposedfaster than bean straw. In terms of mean AWCD (the average well colour development ) of soil microbial communities, a declining order of FCN (Fresh corn straw + nitrogen fertilizer) > FC (Fresh corn straw) >FB (Fresh bean straw), indicating that the soil microbial community in the soil applied with corn straw was relatively high in density and stability, while that in the soil applied with bean straw was lower during the whole decomposition period. No significant difference in microbial AWCD was found between the three treatments (P>0.05), but sharp differences were between treatments different in types of straw and in duration of decomposition (P<0.01). Analysis of effects of microbial community structures on utilization efficiency of the six categories of carbon sources indicates that the predominant populations in the three treatments fed mainly on saccharides and polymers. When decomposition went on, hard-to-decompose substances gradually accumulated in the middle and later stages of the decomposition, showing that the populations were the weakest in utilization of aroma compounds. Polymers could reduce structure stability of the microbial community and affect residual rate of the straws under decomposition. Correlation analysis shows that decomposition residual rate was significantly related to soil pH, organic matter, alkalyic N, readily available K, soil temperature, the utilization of carbon sources, like amino acids and polyamines, and by a certain degree to soil water content and water content of straw. 【Conclusion】FCN with a proper C/N ratio is susceptible to impact of more factors than FB and FC, when decomposing in the field. Therefore, in the practice of returning straw in the field, it is recommended to adjust C/N ratio of the straw incorporated to a proper degree and to apply microbial agents that are capable of degrading the metabolites of polymers, so as to promote decomposition of the straws incorporated and improve utilization rate of the straws returned.