Molten　salt　is　an　important　heat　storage　and　heat　transfer　medium　in　solar　thermal　power　generation　technology　due　to　its　high　heat　capacity,　wide　working　temperature　range,　and　low　cost.　Adding　nanoparticles　(usually　by　the　two-step　method　with　ultrasonic　dispersion)　can　increase　the　specific　heat　of　molten　salt.　Thus,　the　molten　salt　nanofluids　can　increase　the　heat　capacity　and　decrease　the　heat　storage　cost　of　a　solar　thermal　power　generation　system.　However,　nanoparticles　are　easy　to　agglomerate　in　the　molten　salt;　moreover,　after　agglomeration,　the　performance　of　molten　salt　nanofluids　is　degraded.　A　two-step　method　with　high-temperature　melting　in　preparing　molten　salt　nanofluids　is　proposed　in　this　paper.　Molten　salt　nanofluids　were　prepared　by　high-temperature　melting.　The　base　solution　was　a　low-melting　point　molten　salt　and　the　nanoparticles　were　SiO2　with　a　diameter　of　20　nm.　The　specific　heat　was　measured　and　the　nanoparticle　dispersity　was　analyzed.　The　stability　of　the　molten　salt　nanofluids　was　studied,　and　the　results　were　compared　with　those　prepared　by　ultrasonic　dispersion.　The　average　specific　heat　of　molten　salt　nanofluids　prepared　by　high-temperature　melting　was　1.789　J/(g.K),　which　was　close　to　that　of　molten　salt　nanofluids　prepared　by　ultrasonic　dispersion　and　16.4%　higher　than　that　of　pure　molten　salt.　The　molten　salt　nanofluids　prepared　by　ultrasonic　dispersion　showed　poor　thermal　stability　under　high-temperature　conditions,　and　the　average　specific　heat　decreased　by　8.5%　after　only　200　h.　The　thermal　stability　of　molten　salt　nanofluids　prepared　by　high-temperature　melting　showed　a　highly　stable　performance　in　long-time　experiments.　The　variation　of　specific　heat　was　less　than　5%　after　2000　h　under　the　same　high-temperature　experimental　condition.　The　molten　salt　nanofluids　obtained　by　high-temperature　melting　showed　better　stability　and　long　performance　than　those　obtained　by　ultrasonic　dispersion.　Therefore,　the　two-step　method　with　high-temperature　melting　is　stable　and　reliable　for　preparing　molten　salt　nanofluids.