The characteristics of a kind of thinwalled aluminum alloy hollow out part was studied. It is difficult to guarantee its machining accuracy and processing efficiency.The machining technology for the parts and CNC milling tool were designed,and the process and milling tool were applied in actual machining. The results show that the use of the technology and equipment can not only guarantee the part dimension but also the form and position tolerance, reduce the deformation of the part, guarantee the machining quality of the part, and greatly improve the production efficiency.