Efficient removal of fine dust from the exhaust gas is useful to reduce the harm to human health or minimize materials waste. A circumfluent cyclone (CFC) was designed to improve gas-solid separation efficiency and lower pressure drop compared to common cyclone separators. In this work, the flow pattern and the velocity distribution in a CFC was investigated. Commercial computational fluid dynamics software was used to simulate the 3D-gas-flow field using the Reynolds stress model (RSM). The simulation results (such as velocity profile, pressure drop, and separation efficiency) were in good agreement with experimental results. The results show that about 78% of the gas directly flows out of the CFC through the inner cylinder and then from the vortex finder, which greatly reduces the cleaned gas flow path, and thus the friction loss, compared to that of the common cyclone. It also shows that the CFC reduces the shortcut flow near the vortex finder entrance, then would reduce particle escaping. In addition, the discrete particle model (DPM) was used to predict the flow pattern of particles of various diameters.