The invention discloses a cultivation medium capable of increasing the yield of big clitocybe and a preparation method thereof. The cultivation medium comprises nutrient media and cover-soil materials of which the weight ratio is 2-3 to 1; the nutrient media are prepared from, by weight, 60-70 parts of mulberry twig stalk powder, 15-20 parts of tea tree dregs, 8-12 parts of sheep manure, 5-8 parts of bran, 3-6 parts of corn powder, 2-4 parts of phosphorus fertilizer, 0.5-1.5 parts of lime, 1-2 parts of plaster and 0.5-1.5 parts of derris powder; the cover-soil materials are prepared from, by weight, 25-30 parts of fine soil, 12-15 parts of sucrose silt, 2-3 parts of sodium selenite and 1-2 parts of bacillus thuringiensis. The cultivation medium is rich and comprehensive in nutrient, the nutritional requirement of growth development of the big clitocybe can be met, and the cultivated big clitocybe is large in size, high in growth velocity and high in disease resistance; compared with a conventional cultivation medium, mushrooms are picked about 10 days in advance, and the yield is increased by about 20 percent. The raw materials of the cultivation medium are wide and easy to obtain, the cost is low, the production process is simple, and the cultivation medium is suitable for large-scale cultivation of the big clitocybe.