Abstract: To solve the problem of high peak-to-average power ratio caused by underwater acoustic orthogonal frequency division multiplexing algorithm in the complex underwater acoustic channel environment, a low peak-to-average power ratio underwater acoustic multiuser communication algorithm based on Differential Coding Mapping and Single-carrier Frequency Division Multiple Access (D-SC-FDMA), is proposed in this paper. On the transmitting end, the source codes are converted into baseband symbols by differential coding mapping; the baseband symbols are converted into frequency domain symbols by N-point discrete Fourier transform. From the time domain, the data information of each baseband symbol is distributed to the corresponding frequency band and from the frequency domain, the information of each frequency point is all frequency components of all baseband symbols at the frequency value. All symbolic information of the whole frequency band is transferred to the passband by M-point inverse discrete Fourier transform. The cyclic prefix is added and the symbols are transmitted through the transducer. On the receiving end, the cyclic prefix is removed; all the symbols are moved from the passband to the baseband by the M-point discrete Fourier transform; then the frequency domain symbols are converted into the baseband symbols by the N-point inverse discrete Fourier transform; finally, the source codes are estimated by differential de-mapping. Good simulation and experimental results verify the effectiveness of the proposed algorithm.