Highway　maintenance　mileage　reached　5.25　million　kilometers　in　China　by　2021.　Ultra　-thin　overlay　is　one　of　the　most　commonly　used　maintenance　technologies,　which　can　significantly　enhance　the　economic　and　environmental　benefits　of　pavements.　To　promote　the　low　-carbon　development　of　ultrathin　overlays,　this　paper　mainly　studied　the　mechanism　and　influencing　factors　of　several　ultra　-thin　overlay　functions.　Firstly,　the　skid　resistance,　noise　reduction,　rutting　resistance,　and　crack　resistance　of　ultrathin　overlays　were　evaluated.　The　results　indicated　that　the　high　-quality　aggregates　improved　the　skid　and　rutting　resistance　of　ultra　-thin　overlay　by　5%-20%.　The　optimized　gradations　and　modified　binders　reduced　noise　of　ultra　-thin　overlay　by　0.4-6.0　dB.　The　high　viscosity　modified　binders　improved　the　rutting　resistance　of　ultra　-thin　overlay　by　about　10%-130%.　Basalt　fiber　improved　the　cracking　resistance　of　ultra　-thin　overlay　by　more　than　20%.　Due　to　the　thinner　thickness　and　better　road　performance,　the　performance　-based　engineering　cost　of　ultra　-thin　overlay　was　reduced　by　about　30%-40%　compared　with　conventional　overlays.　Secondly,　several　environmentally　friendly　functions　of　ultra　-thin　overlay　were　investigated,　including　snow　melting　and　deicing,　exhaust　gas　purification　and　pavement　cooling.　The　lower　thickness　of　ultra　-thin　overlay　was　conducive　to　the　diffusion　of　chloride　-based　materials　to　the　pavement　surface.　Therefore,　the　snow　melting　effect　of　self　-ice　-melting　was　better.　In　addition,　the　ultra　-thin　overlay　mixture　containing　photocatalytic　materials　could　decompose　20%-50%　of　the　exhaust　gas.　The　colored　ultra　-thin　overlay　was　able　to　reduce　the　temperature　of　the　pavement　by　up　to　8.1　degrees　C.　The　temperature　difference　between　the　upper　and　lower　surfaces　of　the　ultra　-thin　overlay　containing　thermal　resistance　materials　could　reach　up　to　12.8　degrees　C.　In　addition,　numerous　typical　global　engineering　applications　of　functional　ultra　-thin　overlay　were　summarized.　This　review　can　help　better　understand　the　functionality　of　ultra　-thin　overlays　and　promote　the　realization　of　future　multi　-functional　and　lowcarbon　road　maintenance.　(c)　2023　THE　AUTHORS.　Published　by　Elsevier　LTD　on　behalf　of　Chinese　Academy　of　Engineering　and　Higher　Education　Press　Limited　Company.　This　is　an　open　access　article　under　the　CC　BY　-NC　-ND　license　(http://creativecommons.org/licenses/by-nc-nd/4.0/).