The invention relates to a generation method of organic selenium and production method of selenium-rich agricultural product, which utilizes fulvic acid chelated elemental selenium to prepare the organic selenium; the conversion rate of the selenium is high, the plant absorption efficiency of the organic selenium is higher than that of inorganic selenium obviously, the cost is reduced, and the security is increased. The technical scheme adopted by the invention is as follows: the liquid-state active humic acid-H2SO4 is stirred until the pH value reaches 1.5, then, flocculent precipitate is generated; the liquid-state active humic acid-H2SO4 is placed still for 1 hour and is filtered with a screen of 300-500 meshes; the precipitate is used as solid fertilizer, the yellow brown liquid at the upper part is the fulvic acid; the pH value of fulvic acid is adjusted to 2.0-4.0 with potassium hydroxide, then 1-5 percent of selenium powder is added to and mixed with the fulvic acid with adjusted Ph value, the mixture is heated to 60-130 degrees C. under 1.3-2.1 barometric pressure in a reactor , and kept in the temperature for 6-8 hours, and the fulvic acid selenium with 1.3-1.5 mass percent is generated. The solution dissolved for 800-1000 times is sprayed on the surfaces of leaves for 3 times in the flowering and fruit enlargement periods of crops, with 10-15 days between every two times.