NOVELTY - Preparing culture medium for mushroom using microbial bacterial composition, comprises (i) dissolving e.g. molasses, peptone, ferric sulfate and growth factors in excess of water to prepare a culture medium for bacterial strain composition, (ii) inoculating the bacterial strain composition, and culturing to obtain bacterial composition fluid, and (iii) preparing mixed fermentation fluid, carrying out anaerobic fermentation in a fermentation equipment, terminating the fermentation, when white hyphae appears, reducing the pH is to 5.5-5.6, and adjusting the pH using sodium bicarbonate.    USE - The method is useful for preparing culture medium for mushroom.    ADVANTAGE - The method: is environment friendly as it can transform plenty of straw into fertilizer via non-incineration method; completely utilizes the nutrient content of the bacterial composition; and produces the culture medium, which improves the yield of planted mushroom.    DETAILED DESCRIPTION - Preparing culture medium for mushroom using microbial bacterial composition, comprises (i) dissolving (in wt.%) molasses (0.5-1.5), peptone (0.2-0.3), ferric sulfate (0.04-0.06), sodium chloride (0.1-0.3), magnesium sulfate (0.01-0.03) and growth factors (0.5-1.5) in excess of water to prepare a culture medium for bacterial strain composition, with a pH of 6; (ii) inoculating the bacterial strain composition into the culture medium obtained in the step (i) in a weight ratio of 5-10:100, where the bacterial strain composition comprises (in parts by wt.) Bacillus cereus (20-25), Lactobacillus plantarum (30-35), Streptococcus lactis (40-44) and Rhodopseudomonas palustris (1-5), and culturing for 120 hours at 30 degrees C to obtain the bacterial composition fluid; and (iii) preparing mixed fermentation fluid comprising (in parts by wt.) bacterial composition fluid (0.1-0.5), agricultural straw (60-70), livestock manure (35-25) and molasses (4-5), carrying out anaerobic fermentation of the mixed fermentation fluid in a fermentation equipment at 30-35 degrees C, terminating the fermentation when white hyphae appears in fermentation equipment, reducing the pH to 5.5-5.6, and adjusting the pH to 7-7.5 using sodium bicarbonate.