The　application　of　jointless　bridges　has　been　increasing　year　by　year,　because　it　could　reduce　the　lifecycle　cost　and　improve　the　riding　comfort.　The　approach　slab　in　jointless　bridges　does　not　only　have　the　function　of　road　transition　which　is　the　same　as　the　approach　slab　in　bridges　with　expansion　joints,　but　also　transfer　and　absorb　the　deformation　produced　by　the　thermal　expansion　and　contraction　of　the　girder.　The　Grade　Flat　Approach　Slab　(GFAS)　horizontally　placed　on　the　subgrade　is　one　of　the　most　common　types　of　the　approach　slab　in　jointless　bridges.　The　material　placed　between　GFAS　and　subgrade　should　be　able　to　properly　slide　to　reduce　the　stress　in　GFAS.　The　friction　coefficient　between　GFAS　and　sliding　material　is　an　important　parameter　affecting　the　mechanical　behavior　of　GFAS　in　jointless　bridges.　In　this　paper,　the　tests　of　GFAS　with　different　sliding　materials　subjected　to　horizontal　displacement　were　conducted　to　obtain　the　corresponding　friction　coefficients　(from　0.34　to　0.68).　The　mathematical　model　of　bilinear　spring　could　be　adapted　to　simulate　the　friction　function　between　GFAS　and　different　sliding　materials.　One　DeckExtension　Bridge　(DEB)　that　is　one　type　of　jointless　bridges　was　chosen　as　a　case　study.　The　finite　element　model　was　implemented　by　using　MidasCivil　software.　The　influence　of　GFAS　with　different　sliding　materials　on　the　mechanical　properties　of　DEB　under　temperature　variation　was　investigated.　It　can　be　concluded　that　the　influence　of　the　friction　coefficient　between　GFAS　and　sliding　material　on　the　bending　moment　of　DEB　should　be　taken　into　account.　©　20th　Congress　of　IABSE,　New　York　City　2019:　The　Evolving　Metropolis　-　Report.　All　rights　reserved.