The paper presents an object architecture for model-based applications for the steel milling facility automation. The architecture possesses three levels: modeling level, simulation level, and level of inverse problems. Thereby, the usage of reusable model elements and standard software solutions is considered. The main issue of the architecture is to guide the development of model-based automation solutions on low-cost base and to ensure an efficient model maintenance. The technique can generally be applied to scalable facilities in process industry.