This paper takes an iron ore project as the engineering background, simulate the mechanical characteristics of the solidified tailings with PFC, determine the meso-mechanical parameters of the solidified tailings, establish the uniaxial compression numerical model of solidified tailings. On this basis, studied the influence of particle size distribution and particle number simplification on mechanical characteristics of simulated solidified tailings. According to research findings, The average error between the numerical model and experimental results under uniaxial compression is 5.5. proved that the numerical model constructed by this method can effectively predict the uniaxial compressive strength of solidified tailings, and he effect of capturing the flexible and brittle failure mode of the solidified tailings is good, Further evidence that the PFC numerical model is effective and feasible to simulate the solidified tailings; because of different engineering conditions, the size distribution of tailings is quite different, If the size distribution of tailings is wide, The particle size distribution and particle number of tailings can be simplified when establish the numerical model of tailings. Analysis shows, In the case that the selection ratio of model tailings particle group range reaches more than 50%, The simulation of stress - strain curve and failure mode of solidified tailings is good.