A series of drained tests of ISO medium sand were performed to study the onset and formation of shear band. Using the digital image processing technique, the multifunctional triaxial equipment of GDS was improved. Strain isogram and local stress-strain relation at every sampling time point were recorded based on the improved equipment. The onset of shear band was from inhomogeneity of soil, while the inhomogeneous deformation can be induced by end friction and initial defect. Based on results of global stress-strain and local stress-strain relation, the end friction effect was found to have a strong influence on the radial strain. The macroscopic non-uniform sample was obtained by putting silt clay block into sand sample, evolution of shear band during the loading process showed that the discontinuation of stiffness formed at interface of two materials, with inhomogeneous deformation developing, macroscopic continues shear band fully formed.