In　order　to　accurately　simulate　the　temperature　inside　the　box　girders,　we　researched　the　temperature　distributions　on　cross-sections　of　box　girders　by　choosing　appropriate　simulation　methods　of　inner　boundary　conditions.　Taking　a　concrete　box　girder　bridge　as　a　study　case,　we　measured　the　temperature　distributions　on　the　cross-sections　of　box　girders　on　site.　Moreover,　we　developed　finite　element　models　of　the　cross-sections　of　box　girders　by　using　MIDAS　FEA　software　to　analyze　the　influences　of　four　simulation　methods　of　inner　boundary　conditions　(namely,　measured　temperature　method,　ambient　temperature　method,　mean　ambient　temperature　method　and　air　element　method)　on　the　temperature　distributions　on　the　cross-sections　of　box　girders,　and　analyzed　the　average　temperatures　of　the　cross-sections　of　box　girders　under　historically　extreme　temperature　conditions.　The　results　indicate　that　the　hourly　temperature　curves　of　the　cross-sections　of　box　girders　calculated　using　the　finite　element　model　by　the　measured　temperature　method　provide　the　closest　agreement　with　measured　hourly　temperature　curves.　When　there　is　a　lack　of　measured　temperature　data　from　the　inside　of　the　box　girders,　the　hourly　temperature　curves　calculated　using　the　finite　element　model　by　the　air　element　method　provide　the　closest　agreement　with　measured　hourly　temperature　curves.　The　influence　of　four　simulation　methods　of　inner　boundary　conditions　on　the　average　temperatures　and　positive　vertical　temperature　gradients　on　the　cross-sections　of　box　girders　is　negligible.　The　air　element　method　can　be　used　to　analyze　the　temperature　distributions　on　the　cross-sections　of　box　girders　under　historically　extreme　temperature　conditions.　The　air　element　method　is　proposed　to　carry　out　the　research　on　the　temperature　distributions　on　cross-sections　of　concrete　box　girders.　©　2019,　Journal　Press,　China　Railway　Bridge　Science　Research　Institute,　Ltd.　All　right　reserved.