Agent-oriented modeling tools have many deficiencies in uniformity, flexibility, interaction ability and logic verification capability, which hinder the research and design of muti-agent systems. An object-process methodology/multiagent system(OPM/MAS) agent-oriented modeling method is introduced to express the abstractions of the complex system by using graphics and natural language. The function, structure and dynamic behavior of the system can be integrated in a
refinery and unified model, and logic verification is available. OPM/MAS has advantages of flexibility and expressiveness. The application in the production scheduling of the steel industry shows the advantage of OPM/MAS as a modeling method for complex multi-agent systems.