As a new type holemaking process, helical hole milling can effectively reduce the thrust force and improve the quality when machining of Carbon Fiber Reinforced Plastics (CFRP). Therefore, accurate prediction of the cutting force during helical milling of CFRP could be helpful to select the cutting parameters reasonably and reduce the processing defect. Helical milling experimental study was carried out to obtain cutting force and machining quality under different cutting parameters. The empirical formula of thrust force and plane cutting force were derived by using linear regression analysis. Then, after observing the quality of holes, it is found that there were not significant tearing at both the entrance and the export of holes, and the main defect in helical milling of CFRP is the entrance burr. At last, the effect of cutting parameters on the entrance burr is investigated.