Abstract: Thermocline thickness and exergy efficiency were taken as evaluation indicators to conduct experimental study of thermocline heat storage tank. Influence of charging temperature difference, mass flow rate and radial plate-type diffuser structure on performances of the heat storage tank was studied. Results show that the formation and development of the thermocline are mainly affected by the mass flow rate and the diameter of the diffuser, and the influence of charging temperature difference is not significant. The initial thermocline thickness increases with the increase of Reynolds number Re and Froude number Fr. The exergy efficiency can quantitatively reflect the irreversibility of the formation and development process of the thermocline, and it shows a law of rapid rise and then keeping a relatively high level with a slow rise. Exergy destruction of the thermocline storage tank mainly occurs during the formation process of thermocline. Considering the charging duration and the exergy efficiency, the optimization parameters of the charging process are as follows: Reynolds number is 2 372 - 3 320 and Froude number is less than 0.235.