The invention discloses application of melatonin to the improvement of oil content of cyperus esculentus seeds. The application comprises the following steps: A, mixing the melatonin and an additive to prepare a melatonin mother solution with the concentration of 50mmol/L; B, spraying a melatonin aqueous solution on leaf surfaces of cyperus esculentus in the morning of a sunny day, wherein the height of plants is 80cm at the initial stage of forming the seeds; C, determining the oil content of cyperus esculentus seeds at a mature period; D, carrying out oil content comparison and analysis on the cyperus esculentus seeds and a cyperus esculentus control variety which is not sprayed with the melatonin aqueous solution; E, screening melatonin treatment concentration for remarkably improving the oil content of the cyperus esculentus seeds. An experiment result shows that after exogenous melatonin is sprayed, the absorption and metabolic capacities of the cyperus esculentus on nutrient elements can be improved, so that the content of the cyperus esculentus is improved and the quality of the seeds is improved.