Abstract: A characteristic waveform interpolation(CWI) speech coding algorithm at low bit rates based on bi-orthogonal lifting wavelet(BLWT) is proposed in this paper.The complicated characteristic waveform(CW) alignment operation and convolution operation of filter are cancelled by using BLWT-based CW decomposition.The memory of traditional CW wavelet decomposition algorithm is reduced with its inherent situ calculation.The algorithm delay of the traditional CW decomposition based on wavelet transform is decreased by replacing the samples of adjacent frames with the boundary samples of the current frame.Each decomposed component of CW is independently reconstructed and the quantization parameters of CW are flexibly selected according to the human ear's perception.Two types of CWI speech codecs at 1.84 kb/s and 2.32 kb/s are designed based on BLWT.MOS test results show that 2.32 kb/s BLWT-CWI and 2.4 kb/s MELP have similor quality and the performance of 1.84 kb/s BLWT-CWI is slightly less than 2.4 kb/s MELP.Subjective A/B listening tests also show that the quality of 1.84 kb/s BLWT-CWI is better than that of 2 kb/s LIWI (low complex improved waveform interpolation)codec.