Aiming at the economy and security of the positioning system in semi-submersible, a new scheme based on mooring line switching control is presented. Considering the input delay and uncertainty, the guaranteed cost control with input delay is designed to calculate the control forces to resist disturbing forces. Sufficient conditions are established to assure the existence of the guaranteed cost controller in terms of LMI, and the guaranteed cost controller with input delay is
obtained by solving the linear matrix inequality. The simulation result shows that the controller can solve the problems of parameter uncertainties and the input delay, so that it improves the accuracy and performance of the system.