NOVELTY - Optimal basal culture medium, comprises 60-70 pts. wt. corn core, 5-15 pts. wt. wooden meal, 3-8 pts. wt. wheat bran, 0.5-1.5 pts. wt. phosphate fertilizer, 3 pts. wt. lime and 1-3 pts. wt. gypsum.    USE - The basal culture medium is useful for cultivating mushroom (claimed).    ADVANTAGE - The method not only can improve absorption and utilization of selenium content in mushrooms, but also can improve the safeness and purity of selenium-enriched mushroom, and is environmental friendly.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included cultivating mushroom using basal medium, comprising (i) choosing high temperature mushroom as experiment variety based on cultivation season; (ii) crushing radix astragali straw, pre-wetting, adding microbial leavening agent, fermenting, and carrying out softening treatment of straw stick by choosing 5 different softening degree; (iii) adding mushroom into basal culture medium, and adding 15 pts. wt. radix astragali straw into the basal culture medium, carrying out mushroom cultivation, determining polysaccharide content, amino acids and selenium content in mushroom, and determining radix astragali straw, and fermenting the straw for 12-20 days having optimum degree of softening; (iv) choosing radix astragali straw in an amount of 10 pts. wt., 15 pts. wt., 20 pts. wt., 25 pts. wt. and 30 pts. wt., respectively having optimal degree of softening, and adding different proportions into basal culture medium, adjusting the amount of corn core and sawdust added during mushroom cultivation, measuring the content of polysaccharide, amino acids and selenium in mushroom, and determining the optimum addition ratio of straw, to obtain 15-25 pts. wt. radix astragali; (v) choosing polypropylene bags of specification 23 cmx 55 cmx 3 dmm, and producing bag by lining the bag, placing the bags into an autoclave compartment at 121?OC, sterilizing for 3 hours, placing in warehouse, cooling, and inoculating under sterile conditions; (vi) adding strain into bag-containing mushroom, and placing in shed, maintaining suitable temperature and humidity, so as to prevent illumination on mushroom for 25 days, stimulating growth under increased humidity and temperature, and stimulating fruiting, and carrying out fruiting management; and (vii) harvesting once 7 or 8 mature fruiting bodies are grown, and directly harvesting the fruiting bodies with selenium content or drying the fruiting bodies.