Titanium alloy was widely used in the machining of aviation parts. In the deep cavity milling process of titanium alloy parts, the tool rod with large aspect ratio will vibrate. Aiming at the vibration problem of the cutter with large draw ratio, the dynamic model of the designed milling cutter was established based on the Euler-Bernoulli beam theory, and the parameters affecting the dynamic performance of the cutter were analyzed. Based on the analysis of parameters, design of four core shaft models, through the analysis it was concluded that the best core shaft. Then the toolholder model was established, and the static stiffness, natural frequency and dynamic stiffness of the traditional metal toolholder and damping toolholder were compared by finite element analysis. The results show that the static stiffness of the damping toolholder is increased by 62%, the first natural frequency is increased by 21%, and the dynamic stiffness is increased by 135%. The roughness of the machined surface with two kinds of toolholders was tested, and the roughness of the designed composite damping cutter bar is reduced by 45.3%. The designed compound damping cutter bar has certain engineering significance and academic value, and provides certain guidance for the design of machining tools with large length diameter ratio.