Abstract: A collective pitch control strategy based on second-order sliding mode is proposed for a strongly non-linear and strongly coupled offshore floating wind turbine dynamics system,which solves the problem of fatigue structural loads and power fluctuations caused by the motion of the floating support platform due to random disturbances such as wave and wind speed. Uncertain affine nonlinear model of a floating turbine is constructed. The integral sliding surface is designed based on the "rated speed" of the wind turbine,where the " rated speed" is no longer a constant value,but a variable depending on the pitch speed of the platform. A supertwisting algorithm is applied to conceive second-order sliding mode pitch control law. FAST and Matlab/Simulink are used to carry out collaborative simulation. The proposed control strategy is compared with the conventional PI control to verify the effectiveness.Experiments show that the proposed second-order sliding mode pitch control strategy has good control effect on stabilizing the wind turbine power at high wind speeds,restraining the movement of the floating support platform and reducing the blade root load,as well as having a good load reduction effect on the tower.