This study investigated the impact of the different straw-decomposing microorganism inoculant(SDMI)on soil nutrients and labile organic carbon pool in paddy field under smash returning in regions along the Huai river in Anhui，so as to provide a theoretical basis for reasonable application.Four treatments were designed，which included straw returning with optimized NPK fertilization then applied SDMI No.1(SFD1)，or SDMI No.2(SFD2)，or SDMI No.3(SFD3)or nothing(SF)，and the differences among them in soil nutrients，total organic carbon(TOC)，labile organic carbon(LOC)，microbial biomass carbon(MBC)，available labile organic carbon(ALC)，available microbial biomass carbon(AMC)and carbon pool management index(CPMI)were contrasted.The results showed that SFD1 and SFD2 both increase soil alkalystic nitrogen，LOC，MBC，ALC and AMC by 14.3%，18.8%，48.0%，6.5%，33.3% and 15.6%，18.0%，51.0%，5.2%，37.5%，respectively.However，SFD3 significantly reduced the MBC and AMC by 52.2% and 41.7%，when compared with SF.In addition，SFD1 and SFD2 both increased CPMI by 22.4%，respectively.The correlation test indicated that TOC could objectively reflect changes in soil nutrients and soil carbon dynamic.In conclusion，the application of different SDMIs can increase soil nutrients and promote labile organic carbon，and the effects of SDMI No.1 and SDMI No.2 are more obvious.