NOVELTY - Adding cassava lees to improve municipal sludge half-dry fermentation stability comprises (A) adding dehydrated sludge and cassava wine lees mixture to anaerobic fermentation tank; (B) domesticating strain; and (C) continuously adding mixed material to anaerobic fermentation tank, where marsh gas production rate is 9L/gVS.day, anaerobic fermentation tank realizes stable operation, and anaerobic fermenting tank maintain amount of current. Mixed fermented material in inoculation sludge is subjected to methane bacteria domestication.    USE - Method of adding cassava lees to improve municipal sludge half-dry fermentation stability.    ADVANTAGE - The method makes reactor volume reduced by 60-70%, and saves energy consumption, device and land occupation. It reduces viscosity as compared to municipal sludge dry fermentation process. The method also improves mass transfer, nitrogen balance material and production rate; and avoids addition of pH value of alkaline substance after adding dehydrated sludge and cassava wine lees mixture to ferment.    DETAILED DESCRIPTION - Adding cassava lees to improve municipal sludge half-dry fermentation stability comprises (A) adding dehydrated sludge and cassava wine lees mixture to anaerobic fermentation tank; (B) domesticating strain; and (C) continuously adding mixed material to anaerobic fermentation tank, where marsh gas production rate is 9L/gVS.day, anaerobic fermentation tank realizes stable operation, and anaerobic fermenting tank maintain amount of current. The step (A) comprises adding inoculation sludge in anaerobic fermentation tank, and adding dehydrated sludge and cassava wine lees to seed sludge in mixture, mixing and inoculating sludge to form mixed material to ferment; and continuously adding dehydrated sludge and cassava wine lees mixture to anaerobic fermentation tank, and continuously discharging mixture of dehydrated sludge and cassava lees. Mixed fermented material in inoculation sludge is subjected to methane bacteria domestication.