Gas-liquid cylindrical cyclone (GLCC) separator is widely used in the petroleum industry with potential field applications. Its performance is strongly influenced by the inlet configuration. The 27 degrees optimal inclined inlet angle has been experimentally observed for GLCC with the same diameter of body and inlet. For other GLCCs, the effect of inlet angle on flow pattern and their performances have not been investigated. The main target of the current study is to deeply understand the changes of flow pattern with respect to different inclined angles and flow conditions. Twelve GLCCs with different inclined angles were numerically investigated by using the Reynold stress turbulence model to predict the flow pattern with GLCC. The distribution of radial, axial, and tangential velocity profiles and their maximum magnitudes with respect to the change of inlet angle were carefully considered in this study.