In order to realize the automatic trajectory planning of robotic machining, surface segmentation algorithm for aircraft based on the geometric characteristics of the machining model was studied. Based on the analysis of the processing parameter, the segmentation algorithm for triangle mesh based on approximate curvature was proposed, and the maximum curvature or maximum deviation angle of the processing was used as the threshold. After that, adjacent triangle meshes were connected together, which started from an arbitrary patch in the mesh and end when the threshold was reached. As a result, a approximated planar segmentation surfaces was formed. The proposed algorithm was utilized for surface segmentation of a CAD model of aircraft. Its results showed the uniformity of the segmented surface, which could ensure the smoothness of the generated robotic machining trajectory.