The invention relates to a nutrient medium used for reducing the disease incidence of soil-borne diseases of thin-skin melons and a method for preparing the same. The nutrient medium is prepared from the following components in percentage by volume: 38 to 44 percent of vegetable garden soil, 54 to 60 percent of smashed straws and 2 to 3 percent of expanded chicken manure. The method comprises the following steps of: taking the vegetable garden soil, the smashed straws and the expanded chicken manure; showering the smashed straws by using water and then squeezing for drying the straws; uniformly mixing the smashed straws, the vegetable garden soil and the expanded chicken manure to obtain a mixture; piling the mixture into a trapezoidal nutrient medium pile at room temperature or in a greenhouse; and tightly covering the nutrient medium pile by using plastic cloth and performing fermentation to obtain the nutrient medium. Used for planting the thin-skin melons, the nutrient medium not only greatly reduces the disease incidence of the soil-borne diseases but also improves the trophic structure of soil because of increasing the content of organic matter, nitrogen, phosphorus and potassium in the soil by adding the straws into the soil; and besides, the nutrient medium has higher porosity degree and contributes to the growth of roots of plants, so that the plants grow healthily and robustly and the yield is improved.