In the Power Plant Simulation System, Fluid network is widely present. Model accuracy largely determines the merits of the simulation system. The concept of signal flow graph has been introduced into the mechanism modeling process to describe the fluid network. Various structures in the fluid network are classified as node and branch, and the algorithm relationship of node's pressure and According to identify the unknown parameters in the model using the PSO, the influence from parameters of PSO to the process of optimization could be studied. Then the range of unknown parameters could be determined. Optimization could be accelerated, so as to achieve optimal results.