A typical steel plant includes iron-making, steel-making and rolling mills from the upstream to the downstream. The rolling mill can be extended and segmented as hot strip mill and cold strip mill in a large scale steel plant. A steel plant contains lots of automation control systems and process information systems to pursuit process efficiency and production optimization. The control systems and information systems are segmented based on physical model in ANSI/ISA-88 standard, and ranged up the enterprise-wide and down to each process. It is impossible to construct only a stand-alone Manufacturing Execution System (MES) to cope with the very complicated Computer Integrated Manufacturing (CIM) environment. An adequate MES should interface information systems in the plant seamlessly, and eliminate the duplicated pattern functions which exist elsewhere. To build up an MES model for a steel plant, it is essential to gather all MES-related structure elements in the information systems as the first step, and conceive additional MES¡¦ structure elements as the second step. The first step makes our approach different from the traditional stand-alone MES system development methodology. In this thesis, the MES is decomposed from the view points of ¡¥Structure View¡¦ and ¡¥Behavior View¡¦ to obtain Structure Elements and Behaviors. The MES can be fully described based on Structure Elements and Behaviors. Our modeling approach defines a ¡¥Steel Plant MES Architecture Description Language¡¦ in the beginning, and fabricates a ¡¥Steel Plant MES Reference Model¡¦ then. ¡¥Steel Plant MES Reference Model¡¦ includes a set of Architecture Hierarchy Diagram, Structure Element Diagram, Structure Element Service Diagram, Structure Element Link Diagram, Structure Behavior Coalescence Diagram, and Sequence Diagram. This reference model has been introduced to set up a companywide integrated MES in a brand new steel plant to validate the model.