The dynamic mathematical model of a hydraulic screw down AGC system for hot strip mill was established by using system identification technology based on ARX model.The controlling signal from the AGC closed-loop system electro-hydraulic servo valve and the roll gap displacement signal were used as the system's input and output data respectively.Least squares estimation method(LSCE) was applied in model parameter-estimated process

and Akaike information criterion(AIC) was used in model order identification.Comparing the measured output with 3-step ahead predicted model output

the identification model fitting precision could be researched

as also the model validity was examined using residual analysis.The simulation results show that the identification model is valid.The identification model of hot rolling mill AGC system is the basis of the digital computer simulation analysis

which is also the basis of controller optimization design

and it provides an important groundwork to studying the vibration characteristics of rolling mill.