By analyzing the system parameters of the vertical adjustment device of gantry straightener, calculation methods of hydraulic spring stiffness and mechanical load stiffness of this system were obtained, and the coupling characteristic between hydraulic and mechanical load was analyzed, and the comprehensive stiffness and natural frequency without damping of hydraulic servo control system of vertical adjustment device were gotten, and a method to improve response characteristics of system was proposed. It provides theoretical basis for optimization design of hydraulic servo control system of gantry straightener.