Based on the working principle of marine shaft system and the transmission characteristics of hydrodynamic speed adjusting system, the power flow of the transmission system was studied by researching the cooperative relationship of planetary shifting mechanism and guide vane adjustable hydraulic torque converter. The principles of hydrodynamic speed adjusting system for marine shaft system were analyzed to achieve variable-speed constant-frequency. The system dynamics simulation was employed in studying the dynamic characteristics of differential gear train in planetary shifting mechanism. Relating to the random input of speed and torque as the actual work, the stress and strain of differential gear train in condition of variable speed and variable torque transmission were calculated. This work provides an important reference to select the type of hydrodynamic speed adjusting system and determine parameters for the different power generating system. ©, 2015, Huazhong University of Science and Technology. All right reserved.