The effect of gas exhaust shape on the performance, flow pattern, and erosion rate of a gas cyclone was investigated using a numerical model. The results show that the shape of the gas exhaust affects the movement of the vortex core in the gas cyclone. With a change in the shape of the exhaust gas, the axial and tangential velocities changed in the cyclone. The highest turbulent kinetic energy in cyclones was found in the gas exhaust region. The results showed that the diamond gas exhaust exhibited the highest turbulent kinetic energy among the other shapes. In the cases of diamond and square gas exhausts, the size of the Rankine vortex was decreased, leading to a reduction in the centrifugal force of the gas flow and, thereby, cyclone separation efficiency. The lowest erosion rate and highest separation efficiency were found for the cyclone with a circular gas exhaust.