The drawbar mechanism of a motor built-in high speed spindle with ATC is to provide the clamping force to grip the toolholder for high speed cutting.The connection status between the shaft-taper hole and toolholder is important on the spindle design and manufacture.In this paper,contact analyses of the toolholder and shaft-taper hole using contact elements are conducted.The stresses distribution between the toolholder and shaft-taper hole is then obtained and is used for the subsequent finite element modal analysis.The finite element modal analysis results are verified by the experimental modal testing to guarantee the accuracy of finite element model.Non-uniform contact conditions between the shaft-taper hole and toolholder is addressed especially in this study.Different intensities of resistance to the cutting torque due to different clamping forces,coefficients of friction,contact type and contact rate are provided.The deformations on the shaft and toolholder are also studied in this paper.The results are helpful to design a motor built-in high speed spindle with a suitable clamping force for providing the necessary torque to resist the cutting force and to give a suggestion on the manufacture of toolholder and shaft-taper hole.