Abstract: The clamping reliability and clamping force of three-jaw chuck are related to its mechanism and structural parameters.Through the analysis of the composition, transmission principle and clamping characteristics of the three-jaw chuck, the geometric model, helical equation and clamping force model of the end thread are established by using geometric method and numerical method, the structural factors and related parameters that affect the clamping force and clamping reliability of the chuck are studied, and the key problems are discussed.The results show that it is reasonable in theory to use the constant velocity of Archimedes helix to design the three jaw of the chuck mechanism to realize the self-centering clamping of the workpiece. The calculation of low speed and high speed chuck clamping force according to the static force and dynamic static equilibrium method to establish the model is relatively reliable, the key to the clamping reliability is to meet the self-locking condition, that is, the spiral rising angle is less than the minimum friction angle λ < ϕ_min), the ratio of screw pair lead and thread diameter should meet S/d < πμ_min. The effect of chuck structure parameters on clamping force is relatively small, and the inertia force at high speed reduces the actual clamping force and reliability of chuck.The clamping force can be increased by improving the surface quality and lubrication condition of screw pair, and the effect of inertia force can be reduced and the clamping reliability can be improved by appropriately increasing the preclamping force.