Abstract: In order to investigate the long-term structural safety of the manned capsule shell of deep-sea manned submersible under the action of alternating seawater pressure, two titanium alloy shrinkage spherical shells are designed to carry out fatigue test in a deep-sea environment simulator. In order to reduce the damage to the deep-sea environment simulation device and effectively shorten the test time, a dual-ball parallel fatigue test technology using the internal and external pressure difference method in ultra-high pressure deep-sea environment is proposed in the paper, and the loading and unloading test of nearly 7000 cycles is carried out accordingly. The results show that the test technology is long-term effective and reliable, which can provide technical basis and application reference for the same type of tests.