A computational model for flows in the plain-orifice atomizers with chamfered or rounded orifice inlets is established. The volume of fluid (VOF) method with finite volume formulation was employed to capture the liquid/gas interface. A continuum Surface Force (CSF) model was adopted to model the surface tension. The body-fitted coordinate system was used to facilitate the configuration of the atomizers. The evolution of the fluid/air interface and the velocity vector plots for the atomizers are discussed. The discharge coefficients and the spray angles for the atomizers are also compared. The result is explained by the profile of the axial velocity component at the atomizer exit and the evolution of the pressure drop. It is found that the discharge coefficient decreases very rapidly at the early stage of atomization, while the pressure drop has an abrupt rise at that time. With the same Reynolds number based on the orifice diameter and the mean axial velocity at the atomizer exit, the atomizer with a rounded orifice inlet has a larger discharge coefficient and a larger spray angle. For the conditions investigated in the present study, the atomizer with a rounded orifice inlet is beneficial for better atomization of the liquid jet.