The two dimension of numerical model was constructed by CFD（Computational Fluid Dynamics） technology for a series of expansion-chamber in pipeline. Under the initial condition of inlet fluid rate at 2 m/s，as well as emulation calculation and analysis for different lengths and diameters of 40 mm，60 mm，80 mm and 100 mm，corresponded with diameter series of 65 mm，70 mm and 75 mm were carried out. The result indicated that the CFD model could preferably describe the flowing state in the expansion-chamber and the fluent field parameters could be obtained through the model when the length and width of expansion-chamber varied，which，therefore，could provide reference for optimization design for the pipeline with Expansion-chamber.