The floating vertical axis tidal current turbine will be subjected to complex loads when it works in the marine environment, which will cause the whole power generating device to oscillate, affect the working performance of vertical axis turbine, reduce the life expectancy of the whole power generating device, and even make its structure destroyed. Therefore, it is necessary to study the movement and stress of the turbine under complex sea conditions. Using AQWA to simulate the motion response of floating carrier in frequency domain, the frequency domain analysis of the turbine is carried out, and the hydrodynamic characteristics of floating carrier are studied. The strength of the turbine under extreme conditions is analyzed by ANSYS static analysis module. The results show that the flange connection is the position with the largest stress concentration. The wave forces are superimposed on the turbine, and the strength and fatigue life of the flange joint of the main shaft of the turbine are analyzed. The results show that the strength of the flange and the flange bolts meet the design requirements. However, the flange bolts will not meet the expected life requirements under the extreme conditions, so the turbine needs to stop operation under the extreme sea conditions. The analysis and simulation results provide a theoretical basis for the practical application of hydraulic turbines.