Abstract: In response to problems of large data differences and poor repeatability in mechanical performance testing of forage alfalfa stems, tensile tests were conducted on different parts of stem and constitutive equations were established．Functional relationship between stem tensile strength and cross-sectional area was established, and numerical simulation and experimental verification were carried out on stretching process of alfalfa stems．Results showed that tensile strength and cross-sectional area of upper and middle parts of alfalfa stems satisfied a cubic function relationship, while lower part was more similar to a power exponential relationship．Simulation results of alfalfa stem stretching process were experimentally verified, and results showed that stress-strain curve of feed model stem stretching was consistent with simulation results．Simulation result of stem tensile strength was 31.76 MPa, with an error of about 4.09% compared to the experiment．Simulation results had high reliability．Research results could solve complex nonlinear dynamic problems in manufacturing process of stem cutting machines, provide data and theoretical support for design and manufacturing of key components of forage harvesters, and also provide new ideas and methods for study of mechanical properties of other crop stems．