Straightness deformation occurs during the trimming process of long axle forgings, and the compound technology of trimming and correction can realize trimming and correction at the same time. Current composite processes achieved the simultaneous trimming and correction by applying back pressure, and a new flexible trimming correction system was designed to overcome the shortcomings of the existing back pressure method. Then, the hydraulic circuit with plunger cylinder and accumulator was built by configuring the number and distribution of plunger cylinders in the backing plate, and the thrust of plunger cylinder was controlled by adjusting the hydraulic pressure of accumulator to adjust the back pressure during the trimming process. So the back pressure can be effectively applied to different products. Furthermore, the oil was replaced automatically by online oil temperature monitoring and closedloop calculation, and the oil temperature was ensured. Compared with the existing methods, the flexible trimming correction system can achieve flexible back pressure and meet the trimming requirements of different forging products. Thus, it improves the production efficiency and product precision,and reduces the economic investment of equipment and dies.