The　thermodynamic　optimization　of　NaCl-CeCl3　has　been　carried　out　through　CALPHAD　method,　and　a　set　of　reliable　parameters　has　been　obtained　to　supplement　the　thermodynamic　database.　Based　on　Butler＇s　equation　and　thermodynamic　database　established　by　CALPHAD　method,　the　calculated　surface　tensions　of　molten　salt　mixtures　MCl-CeCl3(M　=　Li,　Na,　K,　Cs)　agree　quite　well　with　experimental　results　reported　in　the　literature.　The　model　parameter　beta　was　determined　to　be　0.95,　1.04,　1.09　and　1.12　for　LiCl-CeCl3,　NaCl-CeCl3,　KCl-CeCl3　and　CsCl-CeCl3,　respectively,　by　fitting　the　experimental　data　of　surface　tension　of　these　mixtures,　since　it　is　out　of　the　question　to　get　a　universal　beta　applicable　to　all　molten　salt　mixtures.　The　new　model　proposed　lately　by　Santos　et　al.　to　describe　the　thermodynamics　in　surface　phase　of　liquid　solution　has　been　reduced　to　a　much　simpler　form　which　is　nearly　numerically　equivalent　to　it　by　eliminating　the　derivative　of　molar　surface　area　with　respect　to　pressure.　The　surface　compositions　and　surface　activity　coefficients　from　Butler＇s　equation　were　compared　with　those　from　Santos　model.　For　LiCl-CeCl3　and　NaCl-CeCl3,　the　results　from　the　two　models　are　almost　the　same　due　to　the　similar　surface　tensions　of　LiCl,　NaCl　and　CeCl3.　Whereas　for　KCl-CeCl3　and　CsCl-CeCl3,　the　mole　fraction　of　CeCl3　in　surface　phase　from　Butler＇s　equation　is　overestimated　compared　with　that　from　Santos　model,　leading　to　a　slight　underestimation　of　surface　activity　coefficients　of　CeCl3　and　also　a　slight　overestimation　of　those　of　KCl　and　CsCl,　since　the　surface　tensions　of　KCl　and　CsCl　are　much　smaller　than　that　of　CeCl3.　(C)　2016　Elsevier　B.V.　All　rights　reserved.