Externally　bonded　FRP　for　strengthening　concrete　structures　is　widely　used　in　concrete　structures　strengthening　field.　Many　factors　affect　the　strengthening　quality,　in　which　delaminations　and　air　voids　are　two　especially　important　factors.　At　present　the　most　popular　method　of　inspecting　delaminations　and　air　voids　is　hammer　sounding,　but　this　method　is　slow,　the　inspection　result　is　easily　influenced　by　the　inspector＇s　experience,　and　the　defect　area　can＇t　be　measured　accurately.　In　this　paper　infrared　thermal　imager　is　used,　according　to　the　inspection　results　with　infrared　thermal　imager　in　different　conditions,　the　influence　factors　to　the　inspection　effect　including　surface　infrared　radiation　rate,　wind,　heat　source　type,　heating　time　and　the　test　environment　are　analyzed.　The　research　shows　that　under　right　conditions　using　infrared　thermal　imager　to　inspecting　the　delaminations　and　air　voids　is　a　convenient,　quick　and　accurate　method.