Abstract: The mechanical properties of soybean and other grain bulk materials are important bases for studying the structural behavior and numerical simulation of grain storage facilities. To study the evolution of dynamic characteristics and investigate the applicability of equivalent linear visco-elastic model to soybean bulk materials, a series of dynamic triaxial tests under different confining pressures were conducted for soybean bulk materials. The variation of dynamic stress-strain relationship, dynamic elastic modulus and damping ratio of soybean bulk materials was analyzed. The results show that the dynamic stress-strain relationship of soybeans is nonlinear and hysteresis. The hysteretic loop of the dynamic stress-strain relationship of soybeans shows the viscous characteristics of soybeans, and Hardin-Drnevich equivalent linear viscoelastic model is preferable for describing the dynamic stress-strain relationship of soybean bulk materials. Under different confining pressures, the changes in the soybean backbone curve are basically the same. The dynamic stress amplitude shows a nonlinear growth trend with the increase of the dynamic strain amplitude, and the slope of the backbone curve keeps decreasing. Meanwhile, the slope of soybean backbone curve increases with an increase in the confining pressure, which reflects the strengthening effect of confining pressure. The dynamic elastic modulus reflects the elastic deformation characteristics of the soybean bulk sample under a certain level of dynamic stress. The dynamic elastic modulus decreases with the increase of the dynamic strain amplitude, but it increases with the increase of the confining pressure under the same dynamic strain amplitude. Furthermore, the dynamic elastic modulus predicted by H-D model can reflect the change in the dynamic elastic modulus with dynamic strain amplitude of soybean. The hysteresis curve can reflect the viscosity of the soybean bulk sample, which is essentially a damping effect. The area of the hysteresis curve increases nonlinearly with the increase of dynamic strain amplitude. And the hysteretic energy dissipation capacity of soybean increases with the increase of confining pressure. Soybean damping ratio is between 5% and 20% under different confining pressures. In addition, the damping ratio increases with the increase of dynamic strain amplitude, whereas the damping ratio corresponding to the same dynamic strain amplitude decreases with the increase of confining pressure. This is because the larger the confining pressure, the denser the soybean sample, and the more obvious the elasticity of the soybean sample.