A numerical simulation technique was employed to model the two phase flow in cyclones using computational fluid dynamics (CFD). Three different inlet angles of cyclone, including 45, 0 and -45 degrees were compared to describe the efficiency of the conventional cyclone with the modified inlet angle ones. The results showed that the interaction between solid particles in dilute system could be neglected. The pressure drop was decreased when the inlet angle of the cyclone increased. The cyclone with 45 degrees inlet angle tended to have the lowest pressure drop. The collection efficiency was improved with 45 degrees inlet angle due to high swirling motion of gas flow.