An　audio　enhancement　method　based　on　AAC　bitstream　is　proposed　in　this　paper.　First,　the　improved　weighted　recursive　averaging　(IWRA)　algorithm　is　introduced　to　estimate　the　noise.　Second,　the　beta-order　minimum　mean-square　error　(beta-MMSE)　enhancement　approach　is　employed　to　obtain　the　spectral　amplitude　of　audio　signals.　Finally,　the　IWRA　method　and　beta-MMSE　method　are　applied　into　MPEG　AAC　codec　for　suppressing　the　noises　included　in　AAC　bitstream.　The　objective　and　subjective　listening　test　results　show　that　the　proposed　method　yields　good　noise　reduction　results,　the　performance　is　better　than　reference　methods.