Hydraulic AGC system is one of the key institutions of the strip thickness control in reversing four-high mill, the dynamic performance of hydraulic AGC system will directly affect the accuracy of the strip thickness control. AMESim software was used to establish the position control model of hydraulic AGC system. Applying PID control strategy, the factors affecting the control performance were analyzed. So the performance of the hydraulic AGC system in reversing four-high mill was optimized.