The pressure and velocity of vortex drop shaft spillway were experimentally studied,and the cavitation numbers of the flow in the drop shaft were calculated.Aeration is necessary to set in vortex drop shaft spillway through analysis.Based on the characteristics of flow in the vortex drop shaft spillway,a formula，established on the projectile theory,was presented to calculate the cavity length of annular aeration in the vortex drop shaft spillway. And experiments to survey the cavity length were also conducted. The comparison between the results of the formula and experiments indicated that the formula can be used to predicting the cavity length as a reference in engineering design.After adding the annular aerator,the change of the average-time pressure was not very much.The fluctuating pressure increased,but it was not dangerous to the wall of the shaft downstream,since the frequency distribution was mostly below 5 Hz.
