Abstract: The structural deformation and elastic vibration of the manipulator will be caused by the flexibility of the manipulator arm during the movement, which will reduce the positioning accuracy and motion stability of the manipulator end. It is of great significance to apply structural vibration control method to the vibration suppression of the manipulator. Based on the design idea of variable stiffness active control, an active control method of arm stiffness is proposed. The stiffness of the manipulator is actively changed by changing the axial force of the manipulator arm. The nonlinear deformation of the manipulator is described by the deformation coupling method, and then the variable stiffness dynamic model of the manipulator arm is established by using the assumption mode method and Lagrange equation. Further, numerical simulation is performed to solve the variable stiffness dynamic model of the manipulator arm. On this basis, a single degree of freedom experimental device based on the active control of arm stiffness method is designed, and the vibration characteristics of the manipulator end under different preloading forces are analyzed. Numerical simulation and experimental results show that the vibration amplitude of the manipulator end is suppressed with the increase of preloading force, which verifies the effectiveness of the active control of arm stiffness. The relationship between the vibration response of the manipulator end and the preloading force is established by using the response surface method. Then the preloading force is optimized by using the Subspace Trust-region algorithm based on Interior-reflective Newton Method, and the optimal preloading force is obtained. This study can provide a theoretical basis for the fine dynamic modeling and the vibration suppression of the manipulator, and provide a direction for the study of the rigidization of economical low-stiffness materials, so as to replace the currently used expensive high-stiffness materials with cheap low-stiffness materials.