The invention discloses a microorganism bacterium agent for straw and excrement mixed composting. The microorganism bacterium agent is composed of the following strains: (2-6)*10<10>cfu of hair mould per gram, (2-6)*10<10>cfu of trichoderma virens per gram, (2-6)*10<10>cfu of geotrichum candidum per gram, (2-8)*10<9>cfu of saccharomyces cerevisiae per gram, (3-5)*10<11>cfu of bacillus thermophilus per gram, (2-6)*10<11>cfu of lactobacillus thermophilus per gram, (2-8)*10<10>cfu of white rot fungi per gram, (2-8)*10<10>cfu of monilinia fructicola per gram, (3-7)*10<8>cfu of pseudomonas putida per gram, (2-6)*10<11>cfu of nitrosococcus per gram, (1-4)*10<6>cfu of green algae per gram and (2-5)*10<7>cfu of blue-green algae per gram. The microorganism bacterium agent can promote a straw and excrement mixed aerobatic composting progress, shorten a composting period, improve a composting rotten degree, accelerate biodegradation of organic matters, alleviate ozone generation and diffusion during composting and reduce loss of nutrient substances such as nitrogen, can be applied to composting of different straw and excrement raw materials for composting enterprises and is used for producing bio-organic fertilizers.