In view of the problems of unstable product quality and low production efficiency in aluminum alloy forging process, for automobile aluminum alloy steering knuckle, the automatic forging production line and its control system were designed. Then, based on the forging process of aluminum alloy steering knuckle, the equipment composition and overall layout of aluminum alloy steering knuckle production line were planned, and the action flow of the main equipment in each process was analyzed. Furthermore, the automatic control hardware system of the production line based on PFOFINET bus protocol and the software system based on PLC were designed, the structured program framework based on PLC was proposed, and the action control logic of the aluminum alloy steering knuckle production line was analyzed to solve the problems of unclear program logic, lengthy command and difficult troubleshooting for the automatic forging production line and improve the programming efficiency. The production tests show that the equipment layout of production line is reasonable, the visual control interface is easy to operate, the production cycle reaches 22 s per piece, the equipment operates safely and stably, the failure rate of production line is low, and the product quality is stable.