To obtain the effect of bolt-joint in a theodolite on the dynamic response of system, the nonlinear property caused by assemble connection was researched. A single bolt connection cantilever model was used to analyze the change of structure vibration characteristics from the bolt-joint. Then, the finite element method was employed in the simulation analysis in time domain for the nonlinear vibration characteristics of cantilever model connected by the bolt joint under low pretension, and the phase diagrams under different loads were obtained. With Fast Fourier Transfer method, the super-harmonic resonances under 1/2 natural frequency excitation were pointed out. By an exciter experiment, the response amplitudes by free vibration and forced vibration were given, respectively, and the simulation results were verified. It shows that the greater the excitation magnitude is, the greater the impact from the nonlinear term is. This method has guiding significance for research on nonlinear vibration characteristics of connection structures.