Abstract: The properties and applications in energy conversion technology as catalyst，reaction medium，electrolyte and heat carrier of molten alkali carbonate are briefly reviewed. The eutectic of molten alkali carbonate mixture has lower melting point and higher catalytic activity as compared with single molten salt. The physical properties（e. g. melting point and viscosity）can be optimized by means of adjusting optimal combination of different alkali carbonates，hence the catalytic activity and fluidity of the molten salt can be improved and the solubility of electrode material NiO in molten alkali carbonate can be decreased.