Various types of behaviors of different soils have been predicted by using the finite element method (FEM) with comprehensive constitutive models developed in geomechanics. There are, however, still some problems for the large deformation analyses within the framework of FEM. Numerical instabilities arise due to the distortion of the FE mesh. In this work, deformation analyses of geomaterials using Smoothing Particle Hydrodynamics (SPH) method are carried out. The SPH method belongs to the class of particle methods. In this paper, the analytical accuracy and the stability of SPH method are investigated for deformation analyses of geomaterials which are assumed to be solid or fluid.