Abstract: Minimum shift keying(MSK) signal of very low frequency (VLF) wave is usually employed in submarine communication. The influence of sea waves on communication can not be ignored because of the height of sea wave and the wavelength of VLF wave in sea water are comparative. In this paper, the bit error rate(BER) of differential demodulation is obtained by computer simulation in consideration of sea waves and Gaussian noise. The effect of the height of sea wave and signal-to-noise ratio (SNR) to BER on communication is analyzed futher.