The invention relates to a method for making sludge into nutrient soil through anaerobic fermentation. Through a reasonable compounding ratio and reasonable arrangement of substrates in a fermentation tank, step-by-step purification layers of an odor substrate adsorption layer, a microbial decomposition layer and a plant absorption layer are formed, so that less odor is given off into air, or the odor is prevented from being given off into the air; in addition, a methane collecting system is paved at the upper part of the anaerobic fermentation tank, so that recycling of sludge energy resources can also be realized. Through 12-month long-time anaerobic fermentation, organic matters which are easy to decompose in sludge can be converted into stable humus type substances, and the content of humus is increased by about 25%. The high-temperature stage duration in the anaerobic fermentation process is long, so that original pathogenic bacteria in the sludge can be killed. The sludge is mixed with alkali soil, so that curing and passivating effects on original heavy metal can be achieved, the validity of the heavy metal is reduced by about 50%, besides, the decomposition effect on antibiotics and durable organic compounds contained in the sludge can be achieved, and the harmfulness of the sludge is reduced.