Abstract: This paper presents a study on the effects of asymmetric flaring gate pier Y-shapes on the length of steps-aerated cavity and its negative pressure. We adopted a RNG turbulence model and a VOF model to simulate the water vapor two-phase flows, and used a PISO velocity-pressure coupling algorithm for iterative solution of geometry reconstruction scheme with the unsteady flow approach. For a stepped spillway with asymmetrical Y-shape flaring gate piers, the study covers a flow domain from the reservoir up to the end sill of downstream stilling basin, and focuses on numerical simulations of the length of cavity and its negative pressure in the conditions of gate piers' contraction ratios of 0.598, 0.497 and 0.445. Experimental tests were conducted with the aerated cavity lengths being measured. Comparison of the simulated and measured results shows a good agreement of the cavity length with calculation errors in the range of 9.7%, indicating accuracy and reliability of the present method in successful calculation of cavity length and pressure distribution. The simulations show that as the pier contraction ratio decreases, the cavity length is reduced, and that the length of cavity at the smaller contraction side is four to five times greater than that at the other side. With a decreasing pier contraction ratio, negative pressure on the steps aerated by the air cavity is reduced, but its covering area on the steps expands gradually. At the outer edge of all the steps occurs a negative pressure that takes the lowest value on the vertical face of the first step at the spillway entrance.