Two-tank　molten　salt　heat　storage　systems　are　considered　to　be　the　most　mature　thermal　storage　technology　in　solar　thermal　power　plants.　As　the　key　part　of　the　system,　the　thermal　performance　of　molten　salt　tanks　is　of　great　importance.　An　experimental　thermal　storage　system　with　a　new　type　of　molten　salt　as　a　thermal　energy　storage　medium　has　been　built　to　investigate　the　temperature　distribution　of　molten　salt　inside　the　tank　during　the　cooling　process　from　550　degrees　C　to　180　degrees　C.　The　temperature　distribution　of　the　salt　was　obtained,　which　reveals　that　temperature　stratification　appears　at　the　bottom　of　the　tank　within　the　height　of　200　mm.　The　position,　with　the　maximum　temperature　difference　of　16.1　degrees　C,　is　at　the　lower　edges　of　the　molten　salt　storage　tank.　The　temperature　distribution　was　also　measured　to　deepen　our　understanding　of　the　insulation　foundation,　which　shows　that　the　maximum　temperature　appears　at　the　middle　upper　part　of　the　foundation　and　decreases　radially.　The　heat　losses　of　the　molten　salt　tank　were　calculated　by　the　classical　equation,　from　which　it　was　found　that　the　heat　loss　decreases　from　3.65　kWh　to　1.82　kWh　as　the　temperature　of　the　molten　salt　drops　from　550　degrees　C　to　310　degrees　C.　The　effect　of　temperature　stratification　on　the　heat　losses　of　the　tank＇s　bottom　was　also　analyzed.