Method for preparing marsh gas by fermentation of external invasive plant alternanthera philoxeroides serving as raw material

The invention discloses a method for preparing marsh gas by fermentation of external invasive plant alternanthera philoxeroides serving as a raw material, which comprises the following steps of: mixing pretreated alternanthera philoxeroides and straws, and adjusting the carbon-nitrogen ratio to 20-30: 1; then putting the mixture into a fermentation device for inoculation, wherein the adding amount of the inoculation substance is 10 to 30 percent based on the dry weight of the fermentation materials; adjusting the TS load to between 6 and 10 percent in the fermentation device; and controlling the anaerobic fermentation reaction temperature to be between 25 and 35 DEG C, and stirring the fermentation materials during fermentation, wherein the marsh gas can be generated in 1 to 2 days, and the fermentation period is 20 to 50 days. The method has simple process, is convenient to operate and manage, effectively reduces the threat of the external invasive plant alternanthera philoxeroides, solves the problem of ins