Since SiCf/SiC composite is typical heterogeneous and anisotropic material, the metal material quality evaluation system is not fully appli-cable. There is an urgent need to establish a suitable surface quality evaluation method. Combined with the ultrasonic vibration-assisted milling-grinding test, comparing the stability of the 2D roughness Ra and 3D roughness Sa of the milling-grinding surface, and exploring the influence of the size of the Sa measurement area on the measurement results. Combined with the macroscopic, microscopic and 3D morphology, analyzing and studying the experimental results. Based on the area ratio of the more obvious areas with the appearance of pits on the milling-grinding surface, the analysis and research on the surface quality are carried out. The results show that Sa is more suit-able as the characteristic parameter of milling-grinding surface roughness of SiCf/SiC composites. And the Sa minimum measurement area size is 7mm×7mm. Based on roughness analysis, the milling-grinding surface quality can be further evaluated by combining macro-scopic, microscopic and 3D topography. Using the area ratio of obvious pits on the surface, the quantitative analysis of the area that has a great influence on the surface quality is basically realized.