The invention discloses a beam-column joint connection device of a multi-story fabricated steel structure system, and belongs to the technical field of structural engineering. The device comprises an upper column flange, a joint short column upper end flange, a joint short column lower end flange, a lower column flange, an upper box column, a joint short column, a lower box column, an I beam, a joint short column steel plate, a joint short column transverse connection short steel plate, a joint short column vertical connection steel plate and a beam end vertical connection steel plate, wherein the upper box column and the upper column flange are integrated through shop welding; the joint short column, the joint short column steel plate, the joint short column transverse connection short steel plate and the joint short column vertical connection steel plate are integrated through the shop welding; the I beam and the beam end vertical connection steel plate are integrated through the shop welding. The welding parts can all be finished in a shop, field assembly is performed by using bolts, the fastening work of the bolts is convenient and fast, the construction speed and quality are greatly improved, the device adapts to the development of the assembly type steel structure, and meanwhile the joint is a rigid joint and has high ductility and high bearing capacity.