Abstract: The falling process of small absorber ball in the drop-ball device of HTR absorber ball shutdown system has been studied in this paper.Glass ball with the identical dimension of the actual absorber ball diameter（φ6 mm）,and drop-ball device made of plexiglass tube with the identical inside diameter（φ60mm）of the actual absorber ball falling canal in the core have been applied.Experiments of glass ball falling due to gravity in the air environment have been accomplished.The calculation results coming from Beverloo empirical formula,which has been used to calculate mass flow rate of particle at orifice owing to gravity,agrees well with experimental results in this research with the deviation of 4% to 12%.The angle of repose of the measured glass ball in a ball storage vessels made of plexiglass is about 23.Experimental results showed that glass ball in the vertically above center orifice firstly begin to flow,and then the circumambient particles supply to the orifice center in the ball storage vessels designed with the cone angle of the funnel.Glass balls gradually decline freely and smoothly from ball storage vessels.