In order to research the dynamic property of rolling mill gauge control system in the round, a visible accurate rolling mill model was established, the cosimulation method was proposed based on AMESim and ADAMS joint modeling. The rolling mill entity flexible coupling dynamics model was constructed in ADAMS, which achieved the study of rolling mill load characteristics. The physical model of the hydraulic system was established in AMESim, which achieved a precise modeling and analysis to hydraulic servo system. Both of them implemented data exchange through the interfaces, which ensured the accuracy simulation of the hydraulic system and the authenticity of load system simulation. The system realtime dynamic response and realtime data export thickness were obtained through the cosimulation model. By comparing the simulation output data with measured data, it can be concluded that the model can simulate the dynamic response accurately and can reflect the elastic deformation of mechanical components under heavy loads and the thickness of outlet strip.