For the difficulty of largeaperture deephole machining and the difficult machine ability of TC4 material, the type of machining system and different geometric parameters of the drill bits are optimized and determined. According to the selected geometric parameters, the threedimensional (3D) modeling of the nest drill was performed, and the finite element (FE) software of ANSYS was used to analyze the position of the stress concentration of the bit and the modal frequency of the drill rod. Finally, combined with the results of finite element analysis (FEA), the deephole nesting test was conducted. The test results show that the inner wall of the processing hole has high precision and good chip evacuation, which provides effective tool geometric parameters and machining systems for large diameter deep hole nesting of TC4 titanium alloys.