Investigating　the　thermal　insulation　properties　of　lightweight　geopolymer　concrete　is　essential.　This　paper　aims　to　develop　a　lightweight　aggregate　geopolymer　concrete　(LWAGC)　with　good　density,　compressive　mechanical　and　thermal　insulation　properties.　The　dry　density　of　LWAGC　was　adjusted　by　incorporating　expanded　perlite　(EP).　The　variation　in　physical　and　mechanical　properties　of　LWAGC　with　different　EP　content　was　discussed,　including　dry　density,　P-wave　velocity,　ultimate　compression　strength　and　elastic　modulus.　Based　on　infrared　thermal　imaging　technology,　a　rapid　measurement　method　was　proposed　to　simulate　the　indoor　temperature　change　of　buildings　at　high　ambient　temperatures.　The　thermal　insulation　performance　of　the　LWAGC　with　different　EP　contents　was　further　evaluated.　The　findings　show　that　as　the　EP　content　in　LWAGC　increases,　there　is　a　corresponding　decrease　in　P-wave　velocity,　dry　density,　ultimate　compressive　stress,　and　elastic　modulus.　The　lowest　dry　density　of　LWAGC　reaches　1209　kg/m3　while　the　ultimate　compressive　stress　is　still　larger　than　25.0　MPa,　which　can　used　as　LC25　building　materials　in　load-bearing　structures.　The　results　also　show　that　the　addition　of　EP　can　improve　the　thermal　insulation　properties　of　LWAGC.　The　LWAGC　with　50　%　EP　content　has　the　highest　reduction　rate　of　temperature　and　can　maintain　the　indoor　temperature　lower　than　35　degrees　C　under　high　ambient　temperature,　which　have　potential　application　prospects　in　the　load-　bearing　structures　and　thermal　insulation　of　tall　buildings.