The invention relates to a hydraulic test sealing structure of a pressure container. The hydraulic test sealing structure comprises a container body with a cylindrical cavity, wherein an annular fin is arranged in front of the cylindrical cavity; an annular groove type thin wall is arranged behind the cylindrical cavity; the rear end of the thin wall is hermetically welded with a hydraulic pressure connecting pipe; a sealing core rod penetrates into the cylindrical cavity from back to front and then is hermetically welded with the annular fin; the rear end of the sealing core rod is fixedly connected with a plug; the plug is positioned in the hydraulic pressure connecting pipe and is fixedly connected with the hydraulic pressure sealing pipe; the rear part of the sealing core rod is provided with a drainage cavity which is communicated with the cylindrical cavity; the plug is provided with a water injection hole for communicating the drainage cavity with the exterior. The invention also relates to a mounting and use method of the sealing structure. The invention provides the hydraulic test sealing structure and the mounting and use method aiming at an unconventional pressure container, so that effective sealing of a water outlet of the pressure container is realized, smooth pressure test of the pressure container is guaranteed, and the dimensional accuracy meets the requirements after hydraulic test. The hydraulic test sealing structure can be applied to hydraulic test sealing.