The　research　aims　to　study　the　phase　change　heat　transfer　process　of　the　mixed　molten　salt　in　a　cylinder　tank　with　the　bottom　heating　by　the　numerical　and　experimental　method.　A　VOF　and　enthalpy-porosity　coupled　model　was　used　to　discern　the　phase　change　interface　of　mixed　molten　salt　in　a　bottom　heating　cylinder　tank.　The　results　show　that　the　phase　change　heat　transfer　process　of　molten　salt　is　directly　affected　by　natural　convection　intensity,　while　the　position　of　the　phase　change　interface　determines　the　development　of　natural　convection.　During　the　melting　process,　the　obvious　temperature　gradient　and　the　solid-liquid　interface　fluctuation　can　be　observed,　and　the　melting　time　can　be　reduced　with　the　increases　in　heating　power.　On　this　basis,　the　effects　of　thermophysical　properties　of　PCM　and　heating　mode　on　the　phase　transition　process　are　further　studied.　The　results　show　that　the　melting　time　of　mixed　salt　can　be　increased　by　4.8%　and　4.2%,　respectively,　when　the　specific　heat　capacity　and　latent　heat　of　salts　increases　by　20%,　while　it＇s　thermal　storage　density　can　be　accordingly　increased　by　16.24%　and　3.76%　at　the　same　condition.　Comparing　with　other　heating　mode,　the　bottom　and　side　heating　mode　with　the　smaller　heating　area　(H-star　＜=　0.5)　has　a　faster　heat　storage　rate,　which　can　be　applied　to　the　design　of　the　single　heat　storage　tank.