Abstract: Production conditions and formation mechanism of shear band were analyzed based on modified cam model in finite element program ABAQUS.The results show that strain softening is not the necessary condition of shear band formation in soil.Non-uniform force induced by end restraint and initial defect can cause non-uniform deformation,which is the necessary condition of shear band formation.The physical mechanism of shear band formation is presented that non-uniform force or defect element causes the non-uniform deformation in soil.If the critical bearing capacity of elements on some shear surface is reached,strain energy of other elements will rapidly release while deformation slightly increase.The impact action caused by strain energy releasing leads to rapid deformation increase and load reduction of elements on this section,and then continuous visible shear band is formed.