The present study is mainly focused on proposing an effective way to improve the efficiency of a square cyclone separator. For this purpose, a dipleg is attached under the square cyclone to investigate its effect on the performance of square cyclone. A three-dimensional Computational Fluid Dynamics (CFD) simulation is done by solving the Reynolds-Averaged Navier-Stokes equations with the Reynolds stress model (RSM) turbulence model and applying the Eulerian-Lagrangian two-phase method. The turbulent dispersion of particles is predicted by the application of the Discrete Random Walk (DRW) model. The numerical results demonstrate that using dipleg although produced an increase in pressure drop but it positively enhances the separation efficiency of the square cyclone. Using dipleg significantly increases the separation efficiency of square cyclone especially at higher inlet velocity. This can be more obvious when using dipleg which is minimized the 50% cut size of square cyclone about 26.3%.