Abstract: 【Objective】 To understand the relationship between the anatomical structure of Malus sieversii branches and the resistance to Agrilusmali and provide reference for the breeding and biological control of Malus sieversii. 【Methods】 In this study, insect-resistant and sensitive plants of Malus sieversii were used as experimental materials.The internal anatomical characteristics of the Malus sieversii branches were observed with an optical microscope to explore the causes of the insect-resistant phenotype. 【Result】 Under natural conditions, the anatomical structure of xylem of Malus sieversii branches was analyzed.The vessel density had a greater effect on insect resistance.The vessel density of insect-resistant plants was lower than that of sensitive plants, which were 136.2 and 163.1 n/μm², respectively; xylem thickness and xylem ray width had little effect on insect resistance of Malus sieversii plants.From the anatomical structure of the bark of Malus sieversii, the thickness of the cortex and phloem of resistant and susceptible Malus sieversiiplants were significantly different.The phloem thickness of insect-resistant plants was lower than that of sensitive plants, which were 194.9 and 432.3 μm, respectively; Cortex thickness of insect-resistant plants was higher than that of sensitive plants, which were 1,282.9 and 1,037.7 μm, respectively; there was no significant difference in the thickness of periderm. 【Conclusion】 The anatomical structure of Malus sieversii branches has a great influence on the resistance to insects.The smaller the density of the xylem vessel of the branches, the better the insect resistance; the lower the thickness of the phloem, the higher the thickness of the cortex, and the more obvious the phenotype with insect resistance.