Low　melting　point　molten　salt　is　vital　for　concentrating　solar　power　plants.　In　order　to　obtain　the　low　liquid　operating　temperature　molten　salt,　phase　diagram　thermodynamic　calculation　method　was　used　to　predict　the　eutectic　point　of　the　KNO3-NaNO2-KNO2　system　based　on　the　liquidus　of　the　three　subsystems　using　the　subregular　solution　model　(SSM).　To　confirm　the　calculation　accuracy,　the　ternary　phase　diagram　was　also　predicated　by　FactSage　8.2　software　and　verified　through　experiments.　The　results　of　thermal　analysis　experiments　indicated　that　the　ternary　phase　diagram　calculated　by　SSM　had　the　higher　accuracy.　The　preferred　KNO3NaNO2-KNO2　ternary　molten　salt　had　the　melting　point　of　139.8　degrees　C　and　the　composition　of　42.0　mol%KNO3,　48.5　mol%NaNO2　and　9.5　mol%KNO2.　The　thermophysical　properties　and　thermal　stability　experiments　of　the　preferred　molten　salt　showed　that　it　had　the　excellent　long-term　thermal　storage　capacity.　The　sensible　heat　storage　density　and　economics　analysis　indicated　that　the　preferred　molten　salt　was　the　recommended　medium　for　heat　transfer　and　thermal　storage.　The　results　demonstrated　that　the　phase　diagram　thermodynamic　method　with　SSM　was　an　effective　method　to　screen　the　new　and　the　competitive　candidate　molten　salts.