For floating HATT with variable speed control, a numerical model based on CFD method is proposed to predict the surge force. Compared with the hydrodynamic load of the HATT under the same condition but with fixed speed control, the variable speed control can effectively improve the power coefficient of the HATT. When the surge period is 1.5 s and the surge amplitude is D/8, the average power coefficient increases by 36.36%. But the load fluctuation in terms of the axial load and power coefficients are significantly larger than those with fixed speed control. Based on the hydrodynamic load decomposition model of the HATT with fixed speed rotation and surging motion and the variation law of damping coefficient, the hydrodynamic load prediction method of the HATT with variable speed rotation and surging motion is established. By comparing with the CFD results, it is evidenced that this prediction method can effectively predict the axial load and power coefficients of the HATT. The research findings can provide a reference for the rapid prediction of the hydrodynamic load of the HATT during the actual operation of the floating tidal power station.