A　hiss　noise　reduction　method　used　for　audio　signals　based　on　AAC　bit-stream　in　compressed　domain　was　proposed.　The　input　was　AAC　bit-stream　derived　from　noisy　audio　signals,　and　the　output　was　the　enhanced　AAC　bit-stream　used　for　decoder.　First,　Hiss　noise　was　estimated　by　modified　median　absolute　deviation　(MMAD).　Second,　the　auditory　masking　threshold　and　the　masking　parameters　were　calculated　by　modified　discrete　Flourier　transform　(MDFT).　Finally,　the　parametric　soft-thresholding　method　was　employed　to　obtain　the　enhanced　AAC　bit-stream　which　was　used　to　get　the　enhanced　audio　signals　at　AAC　decoder.　The　objective　and　subjective　quality　testing　results　indicate　that　the　proposed　algorithm　can　effectively　remove　the　Hiss　noise　derived　from　AAC　bit-stream　of　audio　signals　and　obviously　outperforms　the　existing　hiss　noise　reduction　methods.