Cyclones are very popular in industrial applications and separate particles from gas based on centrifugal forces. Their popularity is because of simple geometry, high durability and low operating and maintenance costs. A 3D Eulerian–Lagrangian computational fluid dynamics (CFD) model was developed for the gas-particle flow simulation inside a cyclone. The renormalization group (RNG) k–ε model was used to investigate the effect of turbulence and the particle trajectories were calculated via discrete phase model (DPM). The velocity fluctuations were simulated with discrete random walk (DRW) model to study the turbulent dispersion of particles. In this method, the flow is considered as a continuous phase and particles are considered as a discrete phase. The simulation of the gas-particle flow inside the cyclone was developed by using Ansys Fluent 18.2 and the effects of inlet angle on separation efficiency and pressure drop were investigated. The results show separation efficiency is increased with an increase of particle size. Comparing the results of Azadi [1] with the present work show good agreement in simulation results. Final results show that the inlet angle affects the separation efficiency and the 20º inlet causes the best efficiency respect to 0° and -20º inlet.