The laminar separated flow through a two-dimensional sudden-expansion channel has been investigated numerically. We have examined the relation between flow structure and the dynamic characteristics of the flow. In this report, we performed several trial tests about the two-dimensional symmetric sudden-expansion channel flow using an open source CFD toolbox (OpenFOAM). The calculations were performed for the case of four different expansion ratios α=2, 3, 3.5 and 4 in the range of Reynolds number 20≦Re≦400. The results obtaining by Open- FOAM were compared with our numerical results and with the past reliable results (numerical and experimental results) in the same flow field. The results are in good agreement among them. OpenFOAM confirmed can be actually used for analyzing the same kind of flow field.