To meet the need on machining SiCp/Al surface with high efficiency and accuracy, with electroplated diamond grinding wheel and taking mill-grinding narrow slot as a typical example, the influence of machining parameters and mill-grinding tool on SiCp/Al machined surface roughness was experimentally investigated. The results show that the machining parameters and mill-grinding tool both have significant influence on the surface roughness. The influence of grinding speed on roughness appears saddle-shaped, i.e. decreased first, then increase while the roughness is increased as federate increasing. The grinding wheel without flutes can produce lower roughness than that with flutes. Therefore, higher grinding speed, lower federate with fluteless grinding wheel are recommended. Under the given experimental conditions, the optimum combination of machining parameters are grinding speed of 9.42 m/s and federate of 20 mm/min. And if a fluted grinding wheel will be applied to machine narrow slot, the recommended helix angle of the flutes is about 50° to achieve lower roughness.