To obtain the hydrodynamic loads of a floating horizontal-axis tidal turbine with rotation and pitching motion under the free surface condition, a numerical simulation method based on CFD is established. The inflow direction load, power and pitching moment coefficients at different pitch periods, pitch amplitudes and blade tip-immersion depths were analyzed. The results show that the instantaneous values of the inflow direction load, power and pitching moment coefficients have obvious periodic fluctuations, and the fluctuation amplitude increases with the increase of the pitch frequency and amplitude. On this basis, the damping and additional mass coefficients are obtained based on the least square method. The damping coefficient of inflow direction load and power coefficients fluctuates periodically, and the fluctuation period is equal to the pitch period. The damping coefficient of pitching moment coefficient also fluctuates periodically, and the fluctuation period is not only related to pitch period, but also related to the rotation period of the turbine. The research findings can provide relevant data for studying the coupling motion of floating tidal current energy device and control design of the output electricity.