During the navigation of high-speed multihull under the stochastic wave disturbance, large motion amplitudes of heave and pitch can be caused resulting to the adverse effects, such as the seasickness of crew members, worse control performance and even the system instability, thus a robust $H_{\infty}$ control method has been proposed for the vertical stabilization of high-speed multihull in this paper. Firstly, with the consideration of the uncertainty of system parameters, the vertical control model with applied appendages, i.e. T-foil and flap, has been established. Then, based on the control and theory developed for the stochastic system, the control law can be obtained by utilizing the technique of linear matrix inequality (LMI) which guarantees the defined $H_{\infty}$ performance index, such that the desired control performance and system robustness can be both guaranteed. Lastly, the effectiveness of the proposed method has been verified by numerical simulations, and the motions of heave and pitch have been reduced significantly.