This paper proposes the software optimization for implementing AVS-P3 realtime on ARM 9. The optimization for embedded systems has been recognized as a key issue in improving cost as well as performance. In this work, we describe our experience in optimizing AVS audio decoder based on ARM9. We mainly optimize the inversed IntMDCT, CBC and dequantization modules. The test result shows that the decoding speed improves 10 times than the original AVS audio decoder decoding stereo wave signal with the 128 kbps bitrate and 48 KHz sampling rate. Meanwhile, the memory space is reduced from 130.78 KB to 59.91 KB, achieved 54.2% improvement.