Abstract: In order to verify the effects of different decomposing agents on water oat straw composting, the straw appearance, nutrient content of straw composting and composting products on seed germination index were analyzed, so as to screen out straw decomposing agents suitable for climate conditions of red soil hilly region. The experiment inoculated different decomposing agents into compost with materials of water oat straw, livestock manure and urea, which included following five treatments: Gulin microbiological rotting stem agent (T1), Wobao straw rotten agent (T2), low levels of EM microbial agent (T3), high amount of EM microbial agent (T4), and no addition of decomposing agent as control (CK). The results showed that the change of heap rot was significant in the composting process with the addition of decomposing agents. The C/N with microbial agent treatments decreased to 7.8 − 10.8 after 60 days of composting, while that of CK was 12.7. With the process advancement, pH increased gradually, and water-soluble ammonium nitrogen and nitrate nitrogen increased first and then decreased. At the 60 d of composting, thee germination index was 85.4% − 96.5% with agents while that of CK was 84.6%. The decomposing agent increased the available nutrients of the decomposing products, accelerated the decomposing process of water oat straw, increased the decomposing degree of straw, and reduced the phytotoxicity of straw decomposing fermentation. The low levels of EM microbial agent had the better efficacy.