Abstract: In this paper. three factors concerned during description are put forward:objects described, description tools and describers. The relations between the objects described and describtion tools, as well as the methods for selecting description tools are also discussed. On the basis of having constructed a description tool and built a model of simulation, the author proposes the following methods of constructing simulation models: making the described systems abstract and making them change reasonably, or making them amplified locally; partitioning the systems both physically and logically, and using the top-down design method.