Throttling usually occurs when a fluid passes through an orifice, sometimes even severe cav- itation erosion may occur. In this study, the equation for the cavitation index of a throttling valve was proposed and the cavitation erosion area in the throttle valve was found to change its position with the orifice opening (X). Cavitation features of singular and two-port se- ries throttling grooves were characterized by defining cavitation indexes σ₁and σ₂, because the cavitation index-σ can determine the occurrence and intensity of cavitation. Then the indexes σ₁ and σ₂ included internal geometric parameters and external pressure boundaries were obtained, and cavitation indexes curves σ₁-X and σ₂-X were also plotted. From the curves of the cavitation index, it was observed that cavitation concentration section also would transfer with opening X changes in the U-shaped groove. The depth of the U-shaped groove had a more evident impact on cavitation, whereas the effect of width on cavitation erosion was not so obvious. The intensity of cavitation erosion when the fluid flowed into the orifice section of the U-shaped groove was always larger than that when the fluid flowed away.