The quantization process of MPEG- 4 AAC audio coding standard uses double circ~ation patterns proposed by Brandenburg and a better coding quality and compression ratio can be obtained. But in the process of actual coding, because of too many iteration times of,the method, there will be slower convergence speed, and even deadlock situations. Based on the analysis of MPEG - 4 AAC quantization algorithm, this paper pro- poses a fast improved algorithm which can calculate frequency band of each scale factor. By reducing the process of the external circulation effectively and ensuring the quantizat...