The impingement of fly ashes may lead to erosion of monolithic SCR De-NOx, catalysts. In the present study, DPM (Discrete Particle Model) and CFD (Computational Fluid Dynamics) models were coupled to investigate the erosion behavior in honeycombed SCR De-NOx, catalysts. The effects of particle diameter, particle density, gas velocity, turbulent diffusion, chemical reaction and channel size on catalyst erosion were analyzed in detail. Increasing particle Stokes number and equivalent diameter of channel can mitigate catalyst erosion, while the rise of gas velocity results in the increase of catalyst erosion rate. Turbulent diffusion promotes catalyst erosion caused by particles with low Stokes number, but the effect of turbulence on erosion by particles with high Stokes number is inactive. De-NOx, chemical reaction leads to the increase of gas temperature on the wall region, which slightly prevents catalyst erosion. The simulation results show that inertial impact in the inlet section and turbulent diffusion in middle and outlet sections are the dominant mechanisms for catalyst erosion.