Abstract: Conventional drilling of composites always results in fiber delamination and tear, as a new borehole processing method, orbital drilling has many advantages for composites processing.Considering the practical processing condition in aircraft assembly site, one drilling system including robot as moving carrier, orbital drilling terminal actuators as processing unit and orbital drilling tool was established.The orbital drilling parameters orthogonal test of carbon fiber reinforced plastics (CFRP) was carried out based on this system, and the effects of tool spindle speed, feed per tooth and axial feed depth on cutting force were deeply analyzed.With the defects inspection results, the relationship between cutting force and defects, such as delamination and tear, were investigated.At last, the optimal set of process parameters was obtained.It is verified that thrust force decreases more than 26% after optimation and there are hardly tear and burr formation around the hole exit and entrance, which indicates a better machining quality.