In　this　paper,　the　field　tests　on　agglomeration　and　removal　of　fine　particles　has　been　done　in　a　20t/h　coal-fired　power　plant　with　installing　the　wet　phase　transition　condensation　device.　In　order　to　understand　the　removing　mechanism　of　fine　particle　clearly,　the　effect　of　this　device　on　fine　particle　agglomeration　and　removal　efficiency　were　investigated　with　using　numerical　simulation　method.　The　fine　particle　at　the　inlet　and　outlet　of　this　system　was　collected　with　low　pressure　impactor.　The　particle　size　distribution　was　analyzed　and　characterized　with　Mastersizer　2000.　The　results　showed　that　the　inertial　impaction　are　the　major　impact　mechanisms　for　particles　below　1μm　with　this　wet　phase　transition　agglomeration　dust　removal　technique;　the　interception　of　internal　structure　and　droplets　played　a　dominant　role　in　terms　of　impaction　efficiency　for　particles　above　1μm.　But　for　submicron　particles　ranging　from　0.1μm　to　1μm,　the　increasing　in　vapor　condensation　and　Brownian　diffusion　can　improve　particle　removal　efficiency　significantly,　because　of　the　great　difference　at　flue　temperature.　The　removal　efficiency　of　wet　phase　transition　agglomeration　dust　removal　technique　is　above　80%.　©　2015　The　Japan　Society　of　Mechanical　Engineers.