The　multi-connected　air-conditioning　systems　are　widely　used　not　only　in　houses　but　also　in　large　buildings　in　recent　year　in　China　due　to　their　special　advantages.　But　the　flexibility　also　makes　the　real　performances　of　the　systems　vary　with　different　applications.　A　frequency　inverter　multi-connected　air　conditioner　was　designed　and　assembled.　Some　key　technologies　used　in　such　systems　were　discussed　in　this　paper.　The　performance　and　the　operating　characteristics　were　also　tested　and　analyzed.　Finally,　the　integrated　energy　efficiency　was　calculated　and　the　results　shown　that　the　system　has　a　good　efficiency　in　part　load.