Based on an oilfield project in the South China Sea, the material selection of the subsea multiphase flow meter in the actual application process is systematically studied. After comparison, the carbon steel is selected as the main material and its corrosion resistance is increased by overlaying 625 alloy. A plug-in Venturi structure is designed, and the pressure tube is fabricated by plug welding. On this basis, the overlaying welding and its welding qualification are introduced. The prototype of the subsea multiphase flow meter is evaluated through test verification. The research is of certain reference significance for the subsequent engineering application and optimization of domestic subsea multiphase flow meter.