For medium plate leveler, the constant pressure control can improve the quality and precision of the plates, at the same time, the rack can be protected. A constant pressure control system is put forward for the screwdown system of the leveler, which converts the position control system to the pressure control system at a specific point. For the characteristics of nonlinearity, timevarying and disturbance of the hydraulic system of levelers, the control strategy of auto disturbance rejection with disturbance feedforward is adopted, which can reduce the influences of disturbance forces on the straightening force, improving the control precision of the straightening force and achieving constant pressure control. This control strategy is verified by the Matlab simulation and the hydraulic leveler prototype. The results indicate that the influences of disturbance force are brought down and the stability of the leveler hydraulic system is significantly improved.