The yellowing of citrus leaves is mainly due to the weak root growth, which can not absorb enough nutrients (especially trace elements such as boron, zinc, molybdenum, iron and manganese) to meet the needs of plant growth and development. It is necessary to deeply apply organic fertilizer, improve the soil, make the soil layer deep, loose, fertile and deep-rooted, cultivate developed root groups, enhance the ability to absorb nutrients, provide sufficient and comprehensive nutrients for the growth and development of the above-ground parts, and make the above-ground parts flourish, with dark green leaves and no leaf curling. In addition, fertilization management should be strengthened. In the sprouting stage of new shoots, the water-soluble fertilizer of nitrogen, phosphorus and potassium (20~20~20) and the water-soluble fertilizer of amino acid compound micro-fertilizer should be applied to the roots once in time, and the mixed solution of magnesium sulfate, zinc sulfate, borax, urea, potassium dihydrogen phosphate and amino acid compound micro-fertilizer should be sprayed on the leaves every 7~ 10 day for 2~3 times to improve the plant nutrition level.