The invention relates to a nutrient substrate for reducing the morbidity rate of soil-borne disease of cucumber and a preparation method thereof. The nutrient substrate is prepared from the following components in percentage by volume: 32 to 43 percent of gardening soil, 55 to 64 percent of crushed corncob and 2 to 4 percent of rotten pig manure, wherein the rotten pig manure can be replaced by 3 to 5 volume percent of non-rotten pig manure. The preparation method comprises the following steps of: wetting the crushed corncob with water and squeezing the wet corncob; uniformly mixing the squeezed corncob, the gardening soil and the rotten pig manure or non-rotten pig manure; piling the mixture to form a nutrient substrate stack; and covering the stack with a plastic cloth and fermenting the stack. When the nutrient substrate is used for planting the cucumber, the morbidity rate of the soil-borne disease is greatly reduced and organic matter, nitrogen, phosphorus and potassium content of the soil is increased due to the addition of the corncob. In addition, the nutrient substrate has the advantages of large porosity, contribution to the growth of the root system of a plant and capability of making the plant grow robustly and improving the yield.