In order to clarify the anatomical characteristics of the vegetative organs of ‘Caoyuan No. 4 alfalfa’ with extremely strong insect resistance properties, we selected ‘Caoyuan No. 2 varia alfalfa’ which has antithrips characteristics as a control, and used microscope to compare the anatomical structure characteristics of the roots, stems, and leaves of the two varieties, to reveal the antithrips characteristics of ‘Caoyuan No. 4 alfalfa’ to provide a theoretical basis. The results showed that: (1) the thickness of the cortical parenchyma, the thickness of the endothelium, the thickness of the cambium, the thickness of the xylem and the width of wood rays of the root anatomical structure of ‘Caoyuan No. 4 alfalfa’ were all significantly higher than that of ‘Caoyuan No. 2 varia alfalfa’, in which the wood beam width (159.37 μm) is 1.82 times of ‘Caoyuan No. 2 varia alfalfa’ (P＜0.01). (2) The thick horn tissue thickness (21.4 μm) of the stem of ‘Caoyuan No. 4 alfalfa’ is extremely significantly higher than that of ‘Caoyuan No. 2 varia alfalfa’ (P< 0.01), while the phloem width and pith diameter are significantly lower than that of ‘Caoyuan No. 2 varia alfalfa’ (P< 0.01). (3) The seven indicators of leaf anatomical structure of ‘Caoyuan No. 4 alfalfa’ are significantly higher than that of ‘Caoyuan No. 2 varia alfalfa’ (P< 0.01), and the number of palisade tissue layers (2～3 layers) is extremely obvious higher than that of ‘Caoyuan No. 2 varia alfalfa’ (1~2 layer). Studies have shown that the tissue structure of ‘Caoyuan No. 4 alfalfa’ has obvious insect resistance characteristics, and its tissue resistance is more prominent than ‘Caoyuan No. 2 varia alfalfa’.