To accurately calculate the nonlinear bearing capacity of the CBJ(clamp band joint), through the mechanics behavior analysis of each component in the CBJ, a method for calculating the axial connection stiffness of the CBJ considering the change of preload was proposed. A fine finite element model was established considering the nonlinearity of the structure, and the accuracy of the finite element model was verified by axial tensile stiffness experiment. Combined with the finite element model, the theoretical calculation of the device connection stiffness was modified. Based on the established finite element and computational theoretical model, the influence mechanism of the distribution and variation of the belt tension and the initial belt preload on the device strength and connection stiffness was revealed. The results show that the stiffness calculation model can accurately calculate the axial connection stiffness of the device and predict the failure load of the connection, which has important engineering application value.