Abstract:The discriminant formula is a mathematics formula which can decide whether turbidity current plunges.There are an implicit relation between in the discriminant of plunging point,due to the past researchers ignoring or hard to give the mathematics formula on the vertical velocity distribution at the point which could not directly discrete sediment content from Froude number.With mathematic analysis on surveyed data and experiments,physical figure of vertical velocity distribution was decided by parabola.Based on plunging point data during water and sediment regulation period in Xiaolangdi reservoir in 2001 to 2015,and data from tests on physical model of Xiaolangdi reservoir, empirical coefficient of the vertical velocity distribution formula at the point was acquired with calibration,which revealed the theoretical hypothesis was right.Then the momentum correction factor of turbidity current in reservoir is obtained respectively by 1.2 in theory and 1.13,which were closely.Based on the above research,an improved discriminant formula is validated by the data of flumes by Fan Jiahua^[13],Cao Ruxuan^[14] and Jiao Enze^[15],surveyed data of Xiaolangdi reservoir in 2001 to 2005,and data from tests on physical model of Xiaolangdi reservoir.The prediction results of the formula by data from Xiaolangdi reservoir and Sanmenxia reservoir were pretty well with the surveyed.This could be applied in water and sediment regulation program compilation and numerically simulating in sediment-laden reservoirs.