Abstract: The geysering phenomena is studied experimentally under several cases with different height of upper plenum,diameter of vertical column,initial subcooling,coolant inventory and heating power to investigate their influences on the geysering phenomenon.According to the analysis of experimental phenomenon and data,it is found that the liquid periodically boils and various flow patterns alternately occur in the heating system.The refilling of cooler liquid causes significant change of temperature and pressure in the system.The geysering phenomena can be identified by the ratio of pressure difference and temperature difference of vertical column and is more obvious under greater height of upper plenum,less diameter of vertical column and higher heating power.