Abstract: Molten carbonate salt is a good thermal carrier and reaction medium.Surface tension directly affects the interfacial reaction and the distribution of molten salt in reaction system.On the basis of the ionic radii of the components and Butler′s equation，a calculating model is developed for determining the surface tension of the molten Li2CO3-Na2CO3-K2CO3 carbonate ternary system.The effects of temperature and composition on surface tension of molten salt were investigated.Compared with the calculated values of surface tension as well as the data available in the literature，the results showed that the present model was working well.The surface tension of the pure molten carbonate decreased with increasing the electrostatic potential of cations in molten salt.The surface tension in Li2CO3-Na2CO3-K2CO3 system increased with in increasing of the Li2CO3 content.And with the increasing of the K2CO3 content，the surface tension decreased.

Key words: molten carbonate；surface tension, model；Butler equation