Summary: Development of shear bands in saturated soils is a multi-stage process based on the theoretical and numerical investigations in this paper. The soil is initially in homogeneous shear strain state, and the instability can be characterized by a dimensionless number \(D\). The inhomogeneous distribution of shear strains appears when \(D>1\), and the shear band will initiate and develop gradually. Numerical solutions show that only single shear band that is finally formed in the central region of the specimen even several disturbances (distributed along the specimen) appear in the beginning.