Abstract: The control system based on a linear model has large error and tension fluctuating when the flying gauge changes in tandem cold rolling mills. In order to solve the problem, a PID decoupling control method based on the recursion subsection linear model was presented. Simulations were carried out for a 5-stand tandem cold rolling mill using the method. It is found that the accuracy of AGC system is satisfied and the need of flying guage control can be met.