The　fundamental　aeroacoustic　equation　of　the　centrifugal　impeller　was　established　by　solving　the　inhomogeneous,　uniformly　moving　medium　wave　equation.　Then,　the　Lighthill＇s　acoustic　analogy　theory　and　Powell-Howe＇s　vortex　sound　theory　were　applied　to　the　analyses　of　the　aeroacoustic　sources　of　a　centrifugal　fan.　It　is　shown　that　the　dipole　and　quadrupole　sources　are　the　key　factors　for　the　fan＇s　aerodynamic　sound,　and　the　vortexes　inside　the　fan　flow　field　are　the　uppermost　quadrupole　sources.　For　aeroacoustics　analysis　of　a　centrifugal　fan,　we　proposed　a　theoretical　model,　i.e.　neglecting　the　influence　of　sound-soft　boundary　at　the　inlet　and　outlet　of　a　centrifugal　fan.　The　volute　was　simplified　to　be　a　cylindrical　cavity　with　sound　hard　wall.　Finally,　Green　function　in　the　cylindrical　cavity　space　was　presented,　and　the　aeroacoustic　solution　in　the　centrifugal　fan　was　deduced　in　time-domain　by　using　the　Green　function.　According　to　the　calculated　results　of　the　three-dimensional　unsteady　flow　in　a　centrifugal　fan,　the　corresponding　sound　field　may　be　obtained.