The invention relates to the marsh gas fermentation field, and discloses a method for coproducing alcohol and marsh gas by virtue of cassava and a method for generating electricity by virtue of the marsh gas. The method for coproducing alcohol and marsh gas comprises the following steps: sequentially carrying out crushing, pulp mixing, liquidation, saccharification and fermentation on the cassava,so as to obtain fermented mash; distilling the fermented mash, so as to obtain alcohol and waste mash liquid; cooling the waste mash liquid, inoculating a fermentation strain, and carrying out anaerobic fermentation at 50-70 DEG C for 18-25 days, so as to generate the marsh gas, wherein the anaerobic fermentation is carried out in at least one group of anaerobic fermentation systems, each group of the anaerobic fermentation systems comprises a plurality of anaerobic fermentation units which are connected in series, and multiple groups of the anaerobic fermentation systems are connected in parallel. The method for generating the electricity by virtue of the marsh gas comprises the steps of: preparing desulfurated marsh gas, and burning the desulfurated marsh gas in a high-temperature and high-pressure gas boiler so as to generate steam, wherein the generated steam is used for generating the electricity by virtue of a high-temperature and high-pressure turbine, the high temperature is at least 540 DEG C, and the high pressure is at least 9.8MPa. According to the two methods, the yield of the marsh gas can be remarkably increased, the generating capacity can be increased, and the energy consumption of a whole system can be reduced.