Abstract: The design of two-region pebble-bed reactor core represents one of the main technology orientation of high temperature gas-cooled reactor（HTGR）.The 2-meter experiment vessel is established to carry out the study on the fundamental characteristics of pebble dynamics which include the formation of two-region,mixing zone and stagnant zone,and etc.The result indicates that a steady two-region can be obtained under the experiment condition with a strip of mixing zone exist in the boundary where two kinds of pebbles scatter together.Mixing zone can be reduced effectively with the installing guide plates on the surface.There exists a visible stagnant zone at the bottom of the vessel which will be highly concerned.The experiment summarized the basic pebble behaviour in the reactor core which is randomicity and dispersibility as well as certainty in general.