Pressure test tool and method for narrow closed oil cavity of piston rod with double-layer welding structure

The invention discloses a pressure test tool and method for a narrow closed oil cavity of a piston rod of a double-layer welding structure. Comprising a main hoop, an auxiliary hoop, a fastening bolt pair, a plug assembly and a pressure test joint. The main hoop and the auxiliary hoop are arranged on the outer circle of the piston rod corresponding to the positions of all the circles of radial oil holes respectively. The plug assemblies are arranged in radial oil holes in the outer circle of the piston rod respectively, and the pressure test connectors are arranged in oil holes corresponding to the positions of the two receding holes in the main hoop respectively. According to the pressure test tool and method, the main hoop and the auxiliary hoop can tightly press and seal the welding seam of the plug and the pressure test connector, and the high-pressure withstand test of a piston rod closed oil cavity can be effectively guaranteed; the spring washer serves as pressure test buffering, pressure test stabilit