Abstract: A study of chip rate phase hypothesis adaptive decision feedback equalization algorithm for DS-CDMA underwater acoustic communication is presented.Underwater acoustic communication channel is a delay-Doppler double spreading channel.Fading and Doppler spreading severely degrade the correlation characteristic of the spread spectrum signals,so Doppler shift compensation and equalization are needed before decoding.By applying Space diversity-Doppler compensation-Fast Self-Optimized adaptive decision feedback equalization algorithm into DS-CDMA communication,a chip rate phase hypothesis adaptive decision feedback equalization algorithm for DS-CDMA underwater acoustic communication is proposed and its performance is analyzed with real lake trial data and simulation data.At the price of computational complexity,the algorithm dramatically improves DS-CDMA communication quality.Very low symbol error rate is achieved under fast changing multi-path and Doppler shift condition,and the equalizer is stable under low SNR.The overall performance of this algorithm is satisfactory.