The material system of circulating fluidized bed boiler could be divided into two gas solid two-phase flow that circulates inside and outside. Actually the traditional modeling ways always focus on how to analyze the gas solid two-phase flow from the microscopic point of view. In the paper, the collision and friction between the gas and solid particle is neglected. From a macro point of view, the fluid network model is built by signal flow graph theory, and the algorithm description of nodes and branches have been built. Finally, according to the graph modeling software, the form based on signal flow graph has been built.