The complex underwater environment such as turbulence could cause the posture imbalance of the underwater robot. And it even could damage the stability of the system and cause yaw. Aiming at addressing the issues brought by the large angle of turn and external random disturbance, a normalized proportional synchronization coefficient distribution method was proposed. Firstly, the input of the electronic virtual line-shafting was reconstructed and the reference speed of each driven shaft propulsion motor was calculated in real-time. Secondly, in order to meet the requirements of high dynamics and solve the stability problem of the large speed difference, a finite-time dynamic surface backstepping sliding mode controller was designed. Thirdly, an exponential decay torque observer was designed to obtain the accuracy parameter of torque. Finally, the results show that this method could achieve a good balance between real-time, robustness, and accuracy in dealing with the instantaneous large load variation and the constant nonlinear disturbance.