The　reaction　between　organic　acid　and　triethanolamine　was　discussed.　And　its　effect　on　properties　of　the　flux　comprising　the　two　compounds　as　active　substance　was　analyzed.　The　esterification　between　the　carboxyl　of　organic　acid　and　the　hydroxyl　of　triethanolamine　was　prone　to　occur　when　heated　up　to　an　appropriate　temperature.　In　the　IR　spectrum　for　the　residue　of　the　flux,　the　characteristic　band　for　ester　structure　was　identified.　The　endothermic　reaction　between　the　organic　acid　and　triethanolamine　was　revealed　by　the　differential　scanning　calorimetry　(DSC)　thermogram.　The　content　of　active　substance　in　the　flux　should　be　controlled　to　avoid　excessive　solid　residue　around　the　welding　point,　which　has　adverse　influence　on　the　property　of　the　flux.　The　proportion　of　the　components　of　the　flux　for　Sn-Ag-Cu　solder　was　optimized,　and　a　low-residue　no-clean　flux　with　preferable　integrated　properties　was　developed.