Erosion by particles in monolithic selective catalyst reduction (SCR) processes can reduce the operational life of a catalyst and threaten the performance of the SCR system. We present an integrated approach implemented in two stages to predict the erosion condition of SCR processes. First, a 3D computational fluid dynamics (CFD) model was established for a full-sized SCR reactor to obtain information on the flue gas and ash particles at the entrance of the catalyst layer. Second, the detailed inner catalyst structure layers were simulated using MATLAB and a catalyst erosion model was developed, according to the initial and boundary conditions obtained using the CFD models. Relative cold state tests and erosion measurements were conducted to validate the simulation results. The model was applied to investigate the relationship between the reactor installment, the gas-solid flow field and the catalyst erosion. Moreover, a series of retrofit schemes were implemented to confirm that this method can be used in engineering applications.