The current investigation, determines the effects of rib shape and its parameters on an inner flow in which a circular cylinder exist in the middle. The problem is solved in 2 dimensional methods and the distance from the channel's entrance to cylinder is 125 mm. Ansys 14.5 is used for modeling the geometry and meshing of the problem and for modeling the turbulence the k − ε (realizable) is employed. In this study rib and its four parameters of pitch (p), length (h), rib's height (e) and the distance from the cylinders' head to start of rib (a) in a cavitation flow is investigated. The results show that none of rib's parameters has a direct relation with void fraction. The values for these parameters are different for the maximum or the minimum cavitation; namely if a rib's pitch increases and surpasses a specific value, it will reduce the effect of the previous rib in the flow. In fact, the turbulence eradicates before it become more turbulent by the next rib. On the other hand, if the rib's pitch is too small the flow traps between the two ribs and stagnation happens which is the key element in plummeting the pressure and forming cavity. For other parameters either no correlation with void fraction is observed.