Abstract: In order to analysis relationship between mechanical properties and microstructure of tangled forage stems, then to provide guidance for breeding fine varieties and designing new herbage haverster, four kinds of stems at fruiting stage of perennial forage legumes (Medicago sativa lower cellulose, Erect crownvetch strain and Medicago sativa Gannong No.3, Creeping type crownvetch) were chosen to perform the tensile and shear tests by the electronic testing machine CMT2502. The microstructure of forage stems was observed, and the SEM images of transverse and longitudinal section of forage stem were got by scanning electron microscopy. The results show that forage stem is a typical kind of porous, no-continuous, no-homogeneous and anisotropic composite material. Forage stems have enough strength and good flexibility, and its strength depends on the thickness of thick-walled cells and the numbers of vascular bundles, as well as the connection form and strength of cells in stems. The average Young’s modulus of forage stems in the 4 species are 1?427.3、673.0、1?377.5、441.7 MPa, respectively; The average maximum shearing stress with the slippery angle of 30° are 96.24、60.9、124.1、84.4?N, respectively. The new species of Medicago sativa lower cellulose and Erect crownvetch strain were easier for mechanical harvesting because of high strength, low flexibility and less shearing force.