The invention relates to a nutrient for enhancing plant growth and a preparation method thereof. The nutrient comprises the following components in percent by weight: 20-80 percent of nucleotide salts and deoxynucleotide salts and 20-80 percent of sugar or amino acid. The preparation method comprises the following steps of: preparing nucleic acid from mycelium in side products of a fermentation plant, next, hydrolyzing the nucleic acid into the nucleotide salts and the deoxynucleotide salts, and then mixing the nucleotide salts and the deoxynucleotide salts with the sugar or amino acid. The invention has the advantages that (1) the nutrient has no toxicity, harm, residue and any adverse side effect to plants; (2) the nutrient is beneficial to increase of the yield, the income and the efficiency, and has good effects of enhancing the resistance and improving the quality for plants; and (3) the preparation method has a simple process and low cost and is easy for large-scale production and promotion. The nutrient is widely applied to plants such as grain crops, cotton crops, oil crops, tobaccos, tea trees, fruit trees, vegetables, mushrooms, Chinese medicinal plants, flowers, forests and the like.