Abstract. For the purpose of mill Process Control System (PCS) debugging and optimizing, a new simulation method is used. The actual information of rolling process is gathered and sent to the PCS cyclically. This information is saved by PCS. During simulation process, the actual information is read and playback. The PCS receives actual information just like actual rolling process. The simulation software is developed, and the functions of data gathering, data communication, data saving and playback are realized. The new PCS simulation method avoids the problem of traditional method, and the real site situation can be reappeared for the PCS function debugging.