Abstract: Establishing the normal equivalent properties model of bolted joints by boundary condition, the equilibrium and compatibility conditions. Then obtain the first two natural frequencies and damping ratio by modal testing under the different preload, and identification the relationship between different preload and equivalent stiffness and damping of bolted joints. Finally, establishing the finite element model of including bolted joints by ANSYS soft and obtain the first natural frequencies and damping ratio, the error between the theoretical and experimental results of the model is less than 4. 73% , it can be show the validity and feasibility of the proposed method. Besides, the studied results show that, in the test range of this paper, the stiffness and damping coefficient of the joint surfaces increase with the preload, and further proved the dynamic properties of a mechanical system are strong affected by the properties of bolted joints, especially in the case of the low preload.