Four kinds of leguminous and gramineous forage stems in harvesting period were chosen to perform tensile experiments by the electronic testing machine CMT2502. The cellulose, lignin and protein content of forage stems in different conditions were tested. The microstructure was observed. The SEM images of transverse section were got by scanning electron microscopy. The results indicated that, the stress-strain curve of bottom stems obeyed Hooke’s law; the tensile strength of Bromus inermis was higher than Coronilla varia, but the elastic was smaller; the tensile strength and cellulose contents of Coronilla varia were smallest (13.87%) in the four species. A forage stem is a natural anisotropic polymeric composite. The strength and stiffness of forage stems depends on the content, linking and sequence of cellulose and lignin, together with the thickness of thick-walled cells, the numbers of vascular bundles and the connection and strength of cells in stems.