This paper presents the modelling and simulation of automatic position control (APC) in an 8-high cold rolling mill hydraulic system built by CERI (Capital Engineering and Research Incorporation). Key feature of the rolling mill APC system is introduced. From modelling, the servo valve and cylinder models are built, and from simulation the dynamic response of the system can be predicted for selecting system components and optimizing system performance. As system dynamic response is not only depending on the servo valve but also on all components in the system, root locus method is applied to analyze APC system dynamic response. Simulation results with different parameters are compared. Additionally, compared with a 6-high cold rolling mill APC system, the APC system dynamic responses of CERI 8-high rolling mill can reach better results than those obtained in the 6-high rolling mill system.