Abstract: For determining the mechanical parameters and failure mechanism of cemented sandstone, based on experiments, a micromechanical method based on 3-D particle flow code (PFC3D) was proposed to simulate the gradual failure process considering different particle stiffness ratios to verify the feasibility of the numerical model. The mechanical response of sandstone with different cemented materials was analyzed to further indicate the significance of cemented materials and the applicability of the numerical model. Considering changes in the particle stiffness ratio and the ratio of parallel bond stiffness to particle stiffness, the stress ratio, volume strain, coordination number and number of broken parallel bonds changing with axial strain were discussed and their influences on the Poisson's ratio, initial stiffness and ductility were deeply investigated for the cemented sandstone. Simulation results show that different stiffness ratios have different influences on the micromechanical response of the cemented sandstone. Especially with the decrease in particle stiffness, when the tangential stiffness is larger, the cemented sandstone is more brittle. The larger the ratio of parallel bond stiffness to particle stiffness, the greater the brittleness is, and shear failure is more prone to appear in the cemented sandstone. It is concluded that particle stiffness plays a significant role on the mechanical behavior and deformation ability of the cemented sandstone, and especially is very important to choose micro-parameters and construct a constitutive relation in 3-D numerical modeling for practical reservoir sandstone.