The milling experiments of C/SiC composite with PCD tools are conducted， and surface fo rmation mechanism is analyzed by observing surface/subsurface damages. The effe ct of milling parameters on surface topography and surface roughness is discuss ed with the analysis of cutting force. The results show that C/SiC composite is removed in the mechanism of brittle fracture. Laminated fracture， pull out and f racture in bundle of carbon fiber can be observed on the machined surface. The e ffect of milling parameters on surface roughness is basically the same with that on surface topography. The higher cutting speed can improve the surface quality， th e bigger axial depth of cut will worsen the surface quality and the feed per tooth has n o significant influence on surface quality.