Abstract: In the thin plate slab continuous-casting and continuous-rolling device imported by Handan Iron & Steel Corporation,the stability and responding speed of fast hydraulic actuating mechanism are raised with automatic gauge control (AGC) using long distance hydraulic cylinder combined with step backup plate for hot-rolling plate and strip production. The method of digital sedation was used to investigate the dynamic characteristic of hydraulic AGC system of hot rolling mill in CSP line of Handan Iron and Steel Corporation. On the basis of the math model, the effects of main parameters impact on the dynamic characteristic of system by using the newest software _Matlab were studied.