Abstract: The vortex drop shaft spillway with a blocker installed in the middle of the shaft was proposed to reduce the risk of cavitation,which caused by high flow velocity and low pressure.Hydraulic characteristics such as the flow pattern,pressure,three-dimensional velocity,cavitation number and energy dissipation of the spillway equipped with different blocker are mainly obtained and systematically studied by numerical simulation.The results shows that the degree of shrinkage should be selected reasonably to avoid insufficient discharge capacity or insignificant variation in the flow field;The suitable shrinkage degree is able to reduce the ratio of air-core radius to cross-sectional radius and increases the swirl angle,leading to an increase in wall pressure.The resultant velocity and axial velocity of the upper swirling flow decreases along the shaft wall.The reduced probability of cavitation is attributed to the fact that the contracted structure with pressurization and deceleration effect greatly improve the cavitation number.The setting of blocker effectively reduces the turbulence of the water jump and the water cushion at the bottom of the well,in which the pressure is reduced and evenly distributed.Although the energy dissipation rate in energy dissipation well decreases,the substantial increase in the energy dissipation rate of the swirling flow can make up for the loss.The research results fully reveal the flow field characteristics of the vortex drop shaft spillway with a blocker,which can provide a comprehensive insights for the future research and application.