Simulation system was developed, in order to achieve the purpose of offline functional debugging and optimization for the plate rolling line automation system. For the system, it was designed based on the object-oriented technology. Plate mill line was divided into equipment object, instrument object and plate piece object, in which single object attributes are updated by private service and different objects are associated through public property. Based on process control system platform environment, multi-thread structure was used to meet the simulation requirements of multiple process areas. Time trigger was used to control simulation time step, and actual rolling process data can be generated through data playback method. The process from putting slab online to end of rolling was simulated. The developed simulation system was used for one practical project, and the offline commissioning requirements were satisfied well.