Abstract: The air-conditioning system of deepwater semi-submersible drilling rig directly affects the health of employees and the operation safety of electrical equipment on the platform. For the air-conditioning system equipment selection of a semi-submersible drilling rig in the South China Sea, comparison of the same type of semi-submersible drilling rigs is carried out, and the environmental conditions of the South China Sea are investigated and analyzed. Considering the spatial arrangement of deepwater semi-submersible drilling rig, the environmental conditions and the requirements on vibration, noise and comfortableness in NORSOK standards, the air-conditioning system equipment selection of this platform is accomplished.