The invention relates to the technical field of spaceflight assembling, and particularly discloses an assembling tool and method for ensuring the concentricity of wedge-shaped threaded supporting plate nuts in the annular direction. The assembling tool comprises a bottom hole drilling jig and a rivet hole drilling jig which are used for drilling holes in a separated structure product to install the multiple wedge-shaped threaded supporting plate nuts. The assembling method comprises the following steps that (1), the separated structure product is positioned on an a section of the bottom hole drilling jig; (2), multiple bottom holes are drilled at the small-diameter end of the separated structure product; (3), the bottom hole drilling jig is turned over; (4), the separated structure productis positioned on a b section of the bottom hole drilling jig; (5), multiple bottom holes are drilled at the large-diameter end of the separated structure product; (6), rivet holes in the separated structure product are drilled; and (7), the wedge-shaped threaded supporting plate nuts are riveted. According to the assembling tool and method for ensuring the concentricity of the wedge-shaped threaded supporting plate nuts in the annular direction, the assembling precision of the wedge-shaped threaded supporting plate nuts in the annular direction is greatly improved, the production quality of the separated structure product is guaranteed, smooth butt-joint connection between the separated structure product and other products is achieved, and the production cycle of the separated structure product is shortened.