A robust control method for new type wave compensation systems that based on cable-driven parallel mechanisms were presented. The environmental forces and immeasurable parameters were separated from the dynamic equations and treated as disturbances. Then a sliding mode control law was derived using Lyapunov stability theory. For redundant mechanisms, a tension distribution algorithm based on alternating projection was proposed. When feasible solutions exist, this algorithm leads to a "safe" optimum solution that is kept away from all the boundaries of the tension constraints. Even if no feasible solution exists, a best approximate solution will be got which satisfies the tension constraints. An identification method was also proposed to enhance the practicability of the robust control method. Simulation results show that the proposed theories and methods are effective for such wave compensation systems.