Abstract: MP3 coding has become the most popular coding method for audio signals. The distortions of MP3 coding from time and frequency domain based on experiments are explored. An audio watermarking method is proposed: besides synchronization by extracting host signal, secret bit is embedded by quantizing the proportion of low frequency energy of two sequential frames. Then reference parameter values by evaluation of each embedding frame were suggested. The experiment results show the imperceptablity and the robustness against MP3 with a low bit rate and low sampling frequency and against AAC coding, also with a satisfying capacity.