At　present,　ducted　air-conditioning　(AC)　unit　is　characterized　of　high　efficiency,　convenient　installation,　fresh　air,　less　initial　investment,　etc.　It　has　been　widely　used　in　restaurant,　supermarket　and　factory　workshop.　The　investigation　presented　in　this　paper　was　aimed　at　demonstrating　the　system　construction　and　cold　principle　of　the　ducted　air-conditioning　unit,　illuminating　the　design　and　choose　method　of　condenser　and　evaporator.　This　paper　analyses　advantage　and　disadvantage　of　the　capillary　tube,　single　ported　thermostatic　expansion　valve,　double　ported　thermostatic　expansion　valve.　Especially,　modern　large-scale　buildings　make　indoor　and　outdoor　unit＇　placing　distance　very　far,　how　to　ensure　reliable　running　of　the　system　of　long　tube　is　important　.This　paper　creatively　proposes　a　method　that　making　the　balanced　port　thermostatic　expansion　valve　and　capillary　tube　run　parallel　connection,　which　ensuring　reliable　operation　of　the　system　of　long　tube.　The　author　changes　the　outside　dry-bulb　temperature　of　the　maximum　operating　testing　conditions　to　48°C,　and　the　test　voltage　is　changed　to　the　percent　85　of　the　rating　voltage　as　to　inside　control　standard.　It　can　make　conditioner　achieve　ideal　performance　with　super　load　condition　by　reducing　indoor　cycle　air　flow　rate　and　refrigerant　side　pass.　Finally　the　experimental　results　indicate　that　the　product　design　performance　achieves　the　primal　design　purpose,　and　there　are　many　advantages　in　efficiency.