Freezing　process　of　water　droplet　on　a　cold　surface　is　investigated　in　this　paper.　Microscopevideo　system　is　used　to　observe　its　phenomena.　Thermocouple　is　used　for　the　temperature　measuring　of　the　water　droplet　center.　In　our　experiments,　the　temperature　of　water　droplet　decrease　with　the　temperature　of　cold　surface.　When　the　temperature　is　slightly　lower　than　0°C,　No　obvious　phase　change　is　found.　Obvious　phase　change　occurs　when　the　temperature　of　water　droplet　is　about　-5°C.　The　temperature　of　water　droplet　rises　to　and　keeps　at　that　slight　lower　than　the　triple　point　of　water　simultaneously.　Subsequently　it　decreases　to　that　almost　equal　the　temperature　of　cold　surface　after　the　freezing　front　attains　the　location　of　thermocouple.　A　model　of　this　freezing　process　is　put　forward.　The　results　of　numerical　simulation　base　on　this　model　are　corresponding　with　the　experimental.