The finite element analysis is applied to obtain the contact pressure of the contact surfaces at different speed. Based on the three-dimensional fractal model and Hertz theory the contact stiffness of the double locking toolholder-spindle system is obtained, then the simulation model is built to obtain the contact characteristic of the system at high speed. Based on the theoretical model the influences of the different parameters on the taper-surface contact ratio and the contact stiffness are revealed. Finally, the upper limit of the speed and the reasonable ranges of the draw-bar force, disk-spring stiffness and pre-tightening force are defined. All the research results will be a good theoretical basis for the structural design and optimization of the double-locking toolholder-spindle system.