NOVELTY - Method for improving straw methane yield and reducing methane liquid by methane liquid circulation, involves performing solid-liquid separation of mixed material in an anaerobic fermenting tank, detecting the concentration of ammonia-nitrogen, chemical oxygen demand (COD), biochemical oxygen demand (BOD), pH, zinc ion and copper ion using sensor, adjusting parameter, determining biogas slurry circulation, setting methane liquid recycle ratio to X according to methane liquid measurement index data, where X is more than or equal to 0% and is less than or equal to 100%.    USE - The method is useful for improving straw methane yield and reducing methane liquid by methane liquid circulation.    ADVANTAGE - The method improves the methane yield of straw fermentation by 40-50%, and recycles methane liquid by controlling the methane liquid circulation ratio, reduces methane emission, and is cost-effective and stable in operation.    DETAILED DESCRIPTION - Method for improving straw methane yield and reducing methane liquid by methane liquid circulation, involves performing solid-liquid separation of mixed material in an anaerobic fermenting tank, detecting the concentration of ammonia-nitrogen, chemical oxygen demand (COD), biochemical oxygen demand (BOD), pH value, zinc ion and copper ion using sensor, adjusting parameter, determining biogas slurry circulation, setting methane liquid recycle ratio to X according to methane liquid measurement index data, where X is more than or equal to 0% and is less than or equal to 100%, otherwise, the methane liquid is not recycled, the ammonia nitrogen concentration is C mg/l, if C/15 is equal to N to n, the recycle ratio is that X is equal to (100-N)%, if the ammonia nitrogen concentration C is more than 1500 mg/l, the methane liquid does not recycle, the auxiliary parameter range of the recycle ratio is that BOD is more than or equal to 4000 mg/l, COD is more than or equal to 10000 mg/l, zinc ion is more than or equal to 30 mg/l, copper ion is more than or equal to 6 mg/l and pH is more than or equal to 7.5, when the auxiliary parameter reaches a specified range, the methane liquid does not circulate, the ammonia nitrogen concentration is regulated to be less than or equal to 200 mg/l, the BOD is less than or equal to 500 mg/l, the COD is less than or equal to 1000 mg/l, zinc ion is equal to 0, copper ion is equal to 0 and pH is equal to 6.8.