Abstract: Soybean meal is one of the common food raw materials in the world. During storage, sliding or shear failure occurs between particles, which involves the influences of lateral pressure, wall friction and interference between the silo wall. It may lead to the instability, or even damage of the soil structure. An improved triaxial apparatus was studied, especially for the grain materials. The deformation of the whole and local surfaces can be directly measured by the specified image measuring system.