In the process of aircraft assembly, it is often necessary to finish the large diameter intersection hole. The large diameter of the intersection hole and the poor manufacturability of the material lead to large cutting force and large vibration during processing, and the initial holes between different lugs is not concentric, which leads to uneven force of the tool and easy deviation, and the complex assembly and hole making operation environment leads to the difficulty of using large processing equipment. At present, the main processing method is to use automatic feed drill for chambering and reaming. The hole making efficiency is low, and there are many kinds of tools used and the cost is high. Helical milling is a new hole making method in the aerospace field. In the processing of large diameter holes in difficult to machine materials, it has better hole making quality and efficiency than the traditional drilling, chambering and reaming processes. Especially in the chambering process, the helical milling tool will not be biased by the initial hole, with obvious advantages. Based on the portable helical milling equipment, the reaming and finishing test of large-diameter intersection holes was carried out, the dimensional accuracy of the machined holes and the surface quality of the hole wall are tested, and the integrity of the hole wall surface is further studied. The results show that the accuracy of hole size is better than ± 0.05 mm, and the hole wall roughness is better than R_a1.6 μm, which verify the feasibility of using the helical milling method to achieve the precision machining of intersection holes for aircraft assembly.