This work presents a computational fluid dynamics simulation to investigate the effects of inlet geometry on the pressure drop and particle collection efficiency of a tangential inlet cyclone. Three-dimensional, steady governing equations for the incompressible, turbulent flow inside a tangential inlet cyclone are solved numerically under certain boundary conditions. The continuous gas flow is predicted by solving Navier-Stokes equations using the differential RSM turbulence model. The second phase is modeled based on a Lagrangian approach. The commercial CFD code Fluent was used for numerical analysis. Computational results compared experimental data available in the literature for validation. Various cyclones, each has different geometrical ratio of inlet section, studied in this paper Detail analyses of the effects of inlet geometry on the flow behavior, pressure drop and collection efficiency were given.