Abstract: M-ary and code shift keying (CSK) spread spectrum is generally applied to overcome the spreading gain versus data rate limitation in underwater acoustic (UWA) communication. In addition, the concept of orthogonal M-ary CSK is introduced to UWA communication to gain higher rate. We propose a scheme employing double orthogonal channel M-ary and CSK spread spectrum UWA communication based on Gold sequences owing to its large set, good self and cross correlation. The modulation and demodulation scheme of orthogonal M-ary CSK and the factor which is critical to its performance is described by formula. Furthermore, its bit error rate (BER) curve is investigated via simulation and compared with double channel M-ary CSK. Finally, the validity of simulation is verified in experiment. 1096.8 bps data rate of the proposed communication scheme is realized in 10 kbits volume with no error. It is shown that the proposed method offers significantly improved performance through deduction, simulation, experiment and numerical results.