The transmission shaft made of CFRP pipe is widely used in high-tech fields such as UAV and new energy vehicles because of the excellent performances. The buckling degree of non-axially distributed fibers in CFRP pipe determines its initial bending stress, which affects the axial force and machining damage during drilling process. In this presented paper, a finite element simulation model of CFRP pipe drilling is established, and the influence of pipe diameter on the thrust force and damage characteristics during CFRP pipe drilling is further studied by combining with simulation and experiment. The results show that the established finite element model of CFRP pipe drilling has high reliability. The drilling outlet and inlet of CFRP pipe are easy to produce serious push out delamination and peel delamination under the action of the stripping force of spiral groove and the axial force of drill bit. The drilling axial force and outlet delamination damage show a“ V” trend with the increase of pipe diameter. There are obvious burr and delamination damage at the drilling outlet, and the delamination damage factor changes slightly with the increase of pipe diameter. The stripping  length of the material at the drilling inlet and the maximum deflection of the material at the drilling outlet increase with the increase of the pipe diameter. The maximum stress of the material that contacts the drill bit first decreases first and then increases with the increase of pipe diameter, and reaches the minimum when the inner diameter of the pipe is 12 mm.