Semi-submersible drilling rigs are offshore plants that perform function such as ocean exploration for oil and gas acquisition, drilling and production, storage and unloading of crude oil and gas. Semi-submersible drilling rigs use watertight dampers as emergency buoyancy holders. Since the watertight damper is an emergency shutoff device, it is mainly driven by a pneumatic driving system that can operate without power supply. Pneumatic driving system has highly non-linear characteristics due to compressibility of air and external disturbance such as static and coulomb friction. In this paper, a new control algorithm is proposed for the watertight damper driving system based on the sliding mode control. To evaluate control performance and robust stability of the designed controller, the control results were compared with the results using the state feedback controller. As a result, it was confirmed that rack & pinon type of pneumatic driving system for driving the watertight damper using the sliding mode controller that can obtain excellent control performance against the parameter changes and the disturbance.