Abstract: The development of deep-sea exploration technology is of great significance to the study of global environmental changes, the exploration of life origin, the search for seabed resources, and the assessment of marine pollution, and has become an important direction of today's scientific and technological development. Traditional analytical techniques require seawater to be sampled, stored, and then transferred to a laboratory for analyzing, which not only consume time, but also result in biased results. The in situ detection technology can realize long-term, real-time continuous detection, which can solve the problem of sample storage and improve the detection accuracy. Mass spectrometry has abilities to qualitatively and quantitatively analyze lowconcentration substances, which is suitable for in situ analysis. But compared with ground-based applications, the enormous pressure of the deep ocean brings challenges to the analysis of mass spectrometry in the ocean. Mass spectrometry instruments need to work in a high vacuum environment, which require that the sampling system must be able to withstand the pressure difference between the high-pressure liquid and the high vacuum inside the instrument. In order to realize the application of mass spectrometry detection technology in deep-sea exploration, a membrane sampling device capable of withstanding ultra-high water pressure was developed based on the injection technology of volatile organic compounds and dissolved gases in high-pressure liquid environment. The device processes porous sintered rods, vacuum plugs and sampling stainless steel tubes into an integrated sampling structure through a welding process, then coated a hydrophobic membrane, and used ultra-high vacuum sealant to fix and seal the membrane and sampling structure. Therefore, it is ensured that it has sufficient mechanical structural strength, so that the sample injection device can work directly under ultra-high pressure for a long time. A high pressure test environment was constructed by using a high performance liquid chromatography pump and a back pressure regulator, and the pressure resistance test of the ultra-high pressure membrane sampling device was carried out. The test results showed that the device had worked for more than half a month under water pressure of 40 MPa. The sampling device was applied to the online mass spectrometry system, and the sampling efficiency of benzene series and other substances under different pressures, temperatures and flow rates was tested.