The gas-solid turbulent flow and separation processes in square cyclone separators are numerically modeled by the computational fluid dynamics (CFD) method. The Reynolds stress model (RSM) is used to simulate the gas flow and the Lagrangian model is used to calculate the particle motion. Three types of gas exhaust are investigated, including the circular gas exhaust and two types of square gas exhaust with different arrangement. The simulated separation efficiency and pressure drop of the cyclone with the circular gas exhaust are compared to experimental data to verify the present CFD model. The effect of gas exhaust configuration on the turbulent flow characteristics in the separator is discussed and compared for the three types of gas exhaust. The results show that the separation efficiency increases and the pressure drop decreases when the square gas exhaust is used to take place of the circular gas exhaust of the same cross section.