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Relative to circular throttling port, partial pressure throttling groove is significant for releasing pressure drop contraction in throttling port, and decreasing cavitation probability. For typical non-circumferential throttling ports U groove and V groove, their flow abilities(hydraulic diameters) were studied, and it was observed that for U groove, the flow ability is limited under a larger opening, as actual flow ability is depend on minor hydraulic diameter and it is a fixed value; for V groove, hydraulic diameters has a good linear relationship with port opening that means V groove has a wider flow range than U groove does, in other words, V groove is easier to obtain stable smaller flow rate; based on classic cavitation index, new-form cavitation index calculation formula, which is applicable to partial pressure throttling port,was deduced, and the cavitation indexes of U groove and V groove were calculated respectively, and it was found that whether U or V groove, for different flow directions cavitation indexes are different; when fluid flows from the larger section A1 to section A2 cavitation index near section A2 is remarkly larger than that when fluid reversal. At last, this phenomena was theoretically explained.