Condensation　of　two-phase　flow　inside　a　tube　within　sub-cooled　coolant　injected　show　a　complicated　phenomenon　which　affects　both　the　pressure　drops　from　the　upstream　to　downstream　and　the　void　fraction　distribution　in　tube.　This　phenomenon　always　appears　in　the　T-junction　which　kind　of　structure　could　be　found　in　nuclear　power　plants　design.　The　investigation　about　injection　to　two-phase　flow　in　this　structure　can　help　us　predict　the　hydrodynamic　phenomenon　of　condensation　heat　transfer.　Distribution　of　the　fluid　temperature　and　heat　transfer　coefficient　(HTC)　due　to　fluid-fluid　mixing　and　steam　condensation　had　been　considered　to　be　a　significant　process　which　is　included　in　the　pressurized　thermal　shock　(PTS)　research.　Previous　researches　had　built　the　integral　effect　test　to　analysis　the　effect　of　thermal　mixing.　However,　the　practical　condensate　process　in　T-junction　injected　is　too　hard　to　be　predict　accurately,　which　is　contributed　to　the　structure,　the　geometric　dimension,　the　mass　flow　rate　between　the　main　and　branch　pipe,　the　flow　patterns,　the　void　fraction　of　two-phase　flow,　temperature　of　flow,　pressure,　etc.　We　analyzed　the　process　of　cooling　water　injecting　from　the　branch　pipe　into　a　horizontal　main　pipe,　and　also　focus　on　the　phenomena　of　water　injection　in　steam　or　different　flow　patterns.　We　had　set　some　thermo　couples　inserting　to　the　tube　to　keep　observing　the　temperature　field　inside.　The　initial　conditions　of　the　experiment　about　the　flow　pattern　before　the　injection　includes　stratified　flow,　wavy　flow,　annular　flow　and　dispersed　flow.　We　also　took　the　heat　dissipation　between　the　test　facility　and　surround　into　consideration.　The　experiment　is　a　separate　effect　test　program　which　based　on　the　phenomena　about　condensation　in　T-junction　with　45°　incidence　injection　and　progressed　on　ordinary　pressure.