A coupled method of discrete element method (DEM) and volume of fluid (VOF) is applied to study the hydrodynamics and mixing characteristics in solid-liquid stirred tanks with a free surface. By making cutouts or adding fittings on pitched blade turbine (PBT) blades, five modified impellers are obtained, and named as Boundary-cut (BC), V-cut (VC), U-cut (UC), UC-F and UCC impellers. The power consumption, pumping capacity, pumping efficiency, solids suspension, local solids distribution, flow field structure, fluid velocity profiles, trailing vortex, and turbulent kinetic energy (TKE) are investigated carefully in this paper. Results show that the power number decreases by 18.62–29.91% and the pumping efficiency increases by 2.03–22.18% for the modified impellers when comparing to the classical blade. Moreover, adding fittings on the blades has both positive and negative effects on the impeller performance and the mixing of multiphase flows, which depends on the relative position of the fittings to the rotation direction. In addition, the local gradient of TKE have significant impact on the particle distribution. The smaller the local gradient of TKE is, the more even the solid distribution. The results obtained in this report are helpful to guide the improvement and design of impeller blades.