The invention relates to application and preparation method of a sealwort compound, and fat reducing and weight reducing food and medicine, and belongs to the field of chemistry. The sealwort compoundhas a relatively good inhibition effect on lipase activity, and can be used for preparing products with a lipase activity inhibition effect. The preparation method of the sealwort compound comprisesthe steps that a polygonatum cyrtonema product steamed and prepared nine times is subjected to alcohol extraction and extracted, an extraction agent layer is subjected to first-time elution through asilica column, active components obtained after first-time elution are collected and subjected to second-time elution through a Sephadex LH-20 gel column, and the active components obtained after second-time elution are collected for purification. The preparation method is simple and easy to operate, and the yield of the sealwort compound is high. The invention further provides the fat reducing and weight reducing food or medicine. The raw materials of the food or the medicine comprise the sealwort compound and have certain fat reducing and weight reducing effects.