Abstract: In the operating of the drilling pouring pile, drill design of back-rotating drilling machine is an important element for improving its efficiency. For the difference of the understanding of the drilling craft and the one of auxiliary device for the equipment, some details of the drill design are often ignored, but these details are probably important to improve the efficiency and the qualities of the drilling. This paper discusses these details ignored. By the optimal design for the key point of the drilling structure, the drilling's adaptability in different layers is improved widely. Meanwhile, the optimal design increases the drilling's efficiency and operating quality greatly, reduces its cost too.