Abstract: According to the similarity law,the experiment system of pebble dynamics of two-dimension core in High Temperature Gas-cooled Reactor （HTGR） is established to carry out the study on the rules of pebble dynamics. The issues closely related to the reactor core physics and structure design of HTGR is experimentally studied. The experiment results indicate that the pebble dynamics is random and episodic in microcosmic aspect,but is certain and steady in macrocosmic aspect. The stable state is feasible in this experiment condition,the sizes of two regions change regularly with the variation of the proportion of black balls to the white ones,the steady two-region can be obtained in different proportions of black balls to the white ones,and the proportion in the outlet tube is the same as that in the inlet tube.