Steel plate products have variety of applications such as ships, bridges, architectures, public constructions and mining tools. The quality improvement of heavy steel plate is now of great interest for the safety and reliability purpose. In this respect, the microstructure control realised by optimising the alloying elements has acquired a long term research interests as well as developing the heat treatment process such as quenching, tempering, normalising and annealing. More recent achievement of this kind includes Thermo-Mechanical-Control-Process (TMCP) technique which enables finer microstructures.1) TMCP often requires a complicated temperature control not only for heat treatment process, but also for rolling process, which is called Controlled Rolling (CR). The aim of CR process is to control plate microstructure optimising products’ mechanical characteristics. To do so, the rolling temperature of each pass is strictly defined and thus it tends to require an intermediate cooling in between rolling passes; this sometimes An Online Rolling Model for Plate Mill Using Parallel Computation