NOVELTY - Increasing yield of coalbed methane by exogenous microbes, comprises bacteria enrichment and domestication; exogenous bacteria fermentation and amplification; during the exogenous bacteria culture, using molecular biological methods to measure the quantity and activity of endogenous bacteria in coal bed; and injecting the exogenous bacteria into coal beds.    USE - The method is used for increasing yield of coalbed methane by exogenous microbes (claimed).    ADVANTAGE - The fermentation is carried out on the ground. In the growth exponential phase, microorganisms are injected into the coal bed by drilling high-pressure, and sealed for 35-40 days. The exogenous bacteria are used to activate the original bacteria of the coal bed so as to degrade the coal surface organic matter to generate methane gas. Injection of nutrient solution provides start-up energy for microbial metabolism, so that gas production lag time is shortened. The method is simple to operate, and has small influences on the environment and high adaptability.    DETAILED DESCRIPTION - Increasing yield of coalbed methane by exogenous microbes, comprises (a) bacteria enrichment and domestication: sampling from the municipal wastewater treatment plant anaerobic digestion tank, sludge digestion tank or river anaerobic sediment environment for enrichment culture, subjecting the mixed anaerobic strains after enrichment culture to further domestication to adapt coal mine environment and determination of nutrient solution composition ratio, the element content ratio ranges being: potassium (K): 0.004-0.008 mol/L, phosphorus (P): 0.005-0.009 mol/L, nitrogen (N): 0.015-0.020 mol/L, magnesium (Mg): 0.010-0.020 mol/L and sodium (Na): 0.012-0.018 mol/L; further testing physiological and biochemical indexes and metabolites, and identifying strains to obtain exogenous bacteria, exogenous bacteria comprising: hydrolysis fermentation bacteria, hydrogen-producing acetogenic bacteria, cellulose-decomposing bacteria and methane-producing bacteria; the detection method of physiological and biochemical indexes and metabolite is as follows: (1) microbial growth cycle: spectrophotometer; adaptation period: 1-15 days; logarithmic growth phase: 12-35 days; stabilization period: 30-55 days; the decline phase: 50-60 days; (2) sulfate-reducing bacteria: measured by dihydrogen sulfide (H2S) concentration in the generated, divided into four levels, I: 0-200 ppm; II: 200-1000 ppm; III: 1000-1500 ppm; IV: more than 1500 ppm; sulfate-reducing bacteria and methane-producing bacteria compete nutrients, so when the H2S concentration in the I range, the methane-producing bacteria has the highest activity and the gas yield is the highest; the determination method of metabolites comprises (1) the concentration of methane in the gas: using gas chromatograph to measure methane (CH4) concentration, when the CH4 concentration in the gas is greater than 80%, carbon (CO2) is less than 20%, it in an effectively and economically recoverable range; and (2) volatile fatty acids: measured by HPLC, where the main detection index is acetic acid, the content is 4-14 g/L; (b) exogenous bacteria fermentation and amplification: conducting microbial fermentation in the fermentation reaction tank in the ground plant, amplifying strains and improving the microbial activity; (c) during the exogenous bacteria culture, using molecular biological methods to measure the quantity and activity of endogenous bacteria in coal bed; (d) injecting the exogenous bacteria into coal beds: injecting the fermented liquid into the coal bed by high pressure drilling method, sealing the hole for 35-40 days after injection; detecting methane concentration in the drilled hole, organic acid content changes in mine water, microbial populations, the number and structure changes; and (e) when methane gas concentration reaches economically recoverable value, conducting coalbed methane extraction.