The flooding cap is the key equipment for the pre-commissioning of subsea pipeline. Its deep sea installation operation has high risks and strict requirements, which puts forward higher requirements for the safety performance of structural strength. In addition to bearing loads during installation, the flooding cap also needs to block huge internal pressure in the pipeline during pressure test. Its structural strength and bearing capacity directly affect the safety and reliability of the whole subsea production system pre-commissioning. The flooding cap used in a 1 500 m deep gas field in the South China Sea Lingshui area was taken as the research object. Based on the relevant standards of DNV and NORSOK, elastoplastic finite element modeling of the flooding cap and key pressure components was carried out to analyze the safety strength requirements under different working conditions. The results show that the maximum Von Mises stress of each component of the flooding cap is less than the allowable stress under lifting conditions, and the high stress is mainly concentrated at the bolt connection. Under the impact condition, the flooding cap simulation can meet the installation speed requirement of 0.5 m/s, and the overall structural strength can meet the relevant standards. Under pressure testing conditions, the pressure capacity of the flooding cap is calculated to be 823 bar, and the measured pressure during the pre-commissioning operation of the Linsgshui gas field in the South China Sea is 268 bar, which is far less than its pressure capacity, satisfying the finite element calculation results. The relevant research results can provide theoretical basis and technical reference for the design and field application of flooding cap.