The deepwater semi-submersible platform is very important for the development of deepwater oil and gas fields. The ballast system located at the bottom of the hull plays an important role in controlling the draft and stabilizing the hull balance. Based on the premise of ensuring the safety and stability of the system, it is a big challenge for some offshore engineering companies to achieve the optimal design of balancing the piping stress level, controlling piping weight and overall project economics by selecting the appropriate material on the ballast system . As a case study, a semi-submersible platform hull ballast system piping has been simulated using CAESARⅡsoftware. Three types of piping material, namely plastic-coated carbon steel, copper-nickel, and Fibre-Reinforced Plastic( FRP ), are used in the simulation study. The differences in piping stress level, piping weight control, cabin penetration load, natural frequency and the project economics between the three types of piping material have been compared. The optimal piping material has been recommended, to provide design basis for the piping design of semi-submersible platform hull ballast system in the future.