Abstract: In order to study the influence of milling and grinding process on the machining quality of CFRP (carbon fiber reinforced plastics), the single-layer brazed diamond abrasive router and diamond coated end mill were used during the trimming experiment of T800 carbon fiber reinforced plastics. The difference of the machining quality and occurrence of defects were discussed according to the observation of micro topography and measurement of surface roughness. The results show that surface quality under abrasive machining process is much better than that of milling process. Great pits and resin smearing are observed after milling process, while the section of carbon fiber is visible under abrasive machining process. The discussion shows that the fracture of carbon fiber bundles contributes to the formation of great pits and the continual reaction between flank face and finished surface lead to the occurrence of resin smearing. Grinding is the preferred machining process under the strict requirements for surface quality and processing deficiency.