: Particles movement in laminar and turbulent flows has a lot of applications for combustion, biological, environmental and nanotechnology systems. In this study one separator of solid-gas flow that is called Combined Baffle Quick Separator Device (CBQSD) is simulated by FLUENT. FLUENT is very important industrial software to simulate fluid flows. This software is able to simulate 2 and 3 dimensional fluid flows. In this research, turbulence models of,,, RSM and Lagrange model to trail particles are considered. Dual way phase coupling is used to solve particles flows. By changing parameters such as inlet Reynolds number and the device geometry, numerical results are compared with experimental data, and then the optimized condition for separating particles is introduced.umerical analyses show RNG is not an efficient model, because it failed to show the correct amount of average eed. This model could not reveal exactly vortex and flow separating that is occurred by existing separator baffles and guides in chamber. model shows better result than the previous model. This model displays particles speed more accurately and simulates flow near the wall more reasonable than previous model, although this model could not show particle distribution on baffles. Finally, using the five equations Reynolds Stress Model (RSM), better results was obtained. The result from this model was compared in better agreement with experimental data for velocity and distribution of particles. It is concluded that, this model is a better model to consider for this device. A parametric study was conducted based on inlet velocity, device width (distance between the guide baffles and the separator) and inlet flow rate of particles to the chamber. The results show that by increasing velocity, efficiency grows remarkably. It is noticeable that increasing velocity may cause more cost and may require more facility so that high speed is not recommended for use in industrial. Efficiency decreases due to growing particles diameter sizes, because particles do not have enough time to separate from flow field and they are consequently going out by stream. Increasing particle diameter improves efficiency but more increase may cause lesser increase of efficiency because of a violent inverse flow occurs in separator baffles. The results show that the best efficiency is obtained when particles with small diameter used whilst flow rate increases. Total efficiency of device remains around 90% and it changes infinitesimally. Key Words : Gas - Solid Flow, Particle, Separator, Baffle