The results of investigation of the surface tension of the molten mixture LiF-KF-ZrF4 provided in a wide range of temperatures and concentrations. The surface tension melt was determined by the method of maximum pressure in the gas bubble. Set the effect of the initial ion composition of the mixture on the value of the surface tension. Calculated redundant functions interaction of components in the surface layer (the free energy G ω, entropy S ω, enthalpy H ω).