The　vertical　phase　change　thermal　energy　storage　device　(TESD)　is　one　of　the　important　components　in　the　solar　energy-phase　change　thermal　energy　storage-fresh　air　heating　system,　and　its　charge　and　discharge　performances　have　a　direct　influence　on　the　thermal　efficiency　of　the　whole　system.　Taking　TESD　for　study,　based　on　the　results　of　previous　studies,　and　combining　experimental　and　theoretical　analysis,　the　study　has　a　focus　on　the　influence　of　density　difference　which　is　produced　in　the　process　of　heat　exchange　between　heat　transfer　fluid　(HTF)　and　phase　change　material　(PCM)　on　the　charge　and　discharge　performances　and　thermal　efficiency　of　the　system　for　the　difference　of　the　inlet　and　outlet　ways　of　fluid　when　HTF　flows　into　or　out　of　TESD,　which　provides　reference　for　the　optimal　design　of　the　solar　energy-phase　change　thermal　energy　storage-fresh　air　heating　system.