Abstract: The coding performance of MPEG-4 Advanced Audio Coding(AAC) is highly dependent on the efficiency and convergent speed of the quantization module,but its common rate-distortion controller based on two-loop search algorithm produces poor performance especially at low bit rates.This paper presents a novel quantization optimization algorithm.The new scheme has a one-loop recursive structure,in which the initial quantization step size of current frame is calculated from previous ones through linear prediction,and the adjustment of quantization step size is controlled by BFOS(Breiman,Friedman,Olshen,and Stone) algorithm in which the bit allocation is near optimal.Simulation results show that the performance of the new scheme is significantly better than that of the MPEG-4 AAC Verification Model and the computational complexity is highly reduced compared to BFOS algorithm.