In this work, computational fluid dynamics (CFD) is used to study elbow erosion due to a gas–solid two-phase flow. In particular, the direct simulation Monte Carlo (DSMC) method is used to study the impact of inter-particle collision on the erosion behavior. The two-way coupled Euler–Lagrange method is used to solve the gas–solid flow, and the DSMC method is used to consider the collision behavior between particles. The effects of key factors, such as the particle concentration distribution and inter-particle collision, on the erosion ratio are evaluated and discussed. The effectiveness of the method is verified from experimental data. The results show that the inter-particle collision significantly influences the particle movement path and erosion ratio. When the inter-particle collision is considered, the maximum erosion position is offset. The erosion model proposed by Oka et al., who used the DSMC method, agrees best with the experimental data, and the average percentage error decreases from 39.2 to 27.4%.