Abstract: Discharge vessel is an important equipment in the absorber sphere shutdown system of pebble-bed high-temperature gas-cooled reactor. The visualization pneumatic conveying test of the optimized fluidizing discharge vessel was performed at ambient temperature and pressure by using glass balls instead of absorber sphere on a positive pressure system. Experimental results show that the performance of the optimized fluidizing discharge vessel is stable and reliable. With the increase of gas velocity from 8 m/s to 29 m/s, the flow rate of the glass sphere increases from 4.7×10⁴min^-1 to 1.25×10⁵min^-1 and then remains constant. The solid-gas mass flow ratio increases first and then decreases with the increase of gas velocity. The pressure drop of discharge vessel increases first and then decreases and then increases again with the increase of gas velocity. When the gas velocity is above 19 m/s, the process is a stable dilute-phase pneumatic conveying, in which the pressure drop of the vertical tube increases slowly.