Single carrier modulation with time-domain equalization (SC-TDE) in underwater acoustic channel is sensitive to receiver parameters and its computational complexity is very high. Orthogonal frequency division multiplexing (OFDM) signal has high peak-to-average power ratio (PAPR) and is sensitive to Doppler shift. Aiming at these problems, this paper proposes the pseudo-noise (PN)-based single carrier block transmissions through underwater acoustic channels and corresponding receiver algorithms. The receiver employs PN signals for residual Doppler shift estimation, and channel estimation. A low complexity T/4 fractional iterative frequency domain equalizer is introduced to improve the system performance. One underwater acoustic communication system has been designed and tested in a lake in November 2011. At a distance of 1.8 km under a complex channel condition, the useful data rates of around 1500 and 3000 bps are achieved with un-coded bit error rates 10-2–10-4 in the lake experiment.