The invention relates to a straw mushroom nutrient, which consists of the following components by weight percent: 35%-55% of cotton hull powder, 25%-45% of straw powder, 10%-16% of bran, 1.5%-2% of dry dairy manure, 0.5%-1% of bagasse, 0.5%-1% of lime, 0.5%-1% of gypsum, 1.5%-2% of wheat straw, 0.1%-0.3% of carbendazim, 0.1%-0.3% of calcium carbonate, 0.1%-0.3% of mold resisting liquid and 0.5%-0.8% of ammonium bicarbonate. The method for preparing the straw mushroom nutrient comprises the following steps: the cotton hull powder, the straw powder, the bran, the dry dairy manure, the bagasse and the wheat straw are taken according to a proportion, mixed together and poured into a pulverizer to be pulverized into a mixture with granules of about 80 meshes; the mixture is taken out; the lime, the plaster, the carbendazim, the calcium carbonate, the mold resisting liquid and the ammonium bicarbonate are added to the mixture based on a certain proportion; the new mixture is poured into a stirrer to be stirred for about 60 min and then taken; water is added to the stirred mixture at the ratio of 1:1.2-1.4 to evenly be stirred; and the stacked mixture is stacked to be fermented for 10-12h, therefore, the qualified straw mushroom nutrient is prepared.