A combined model integrating the floating turbine structure with simplified aerodynamic characteristics has been developed for the design of blade pitch control. This model employs a second-order super-twisting sliding mode control strategy to coordinate collective pitch control actions, thereby mitigating the fatigue structural loads induced by the motion of the floating turbine structure. The universal affine model, which incorporates platform dynamics, is derived from an approximation of the combined model and is utilized in the design of the sliding mode surface for the control system. A joint simulation using OpenFAST and Matlab/Simulink has been executed, demonstrating that the proposed method significantly outperforms traditional pitch controllers in controlling the motion of the floating platform and the fore-aft tower top motion, while also enhancing power stability.