The utility model discloses a rigid connection mechanism for a large-span steel structure beam and a concrete column of a fabricated building, and aims to provide the rigid connection mechanism for the large-span steel structure beam and the concrete column of the fabricated building, which is high in assembly efficiency. The connecting structure comprises a reinforced concrete column, a steel beam and a connecting mechanism for connecting the reinforced concrete column and the steel beam, the connecting mechanism comprises a steel plate sleeve located at the upper end of the reinforced concrete column and poured and shaped together with the reinforced concrete column, a connecting plate arranged on the steel plate sleeve and used for being connected with the steel beam, a plurality of bolts used for being connected with the steel beam and the connecting plate, and a plurality of opposite-pull screws. The steel plate sleeve comprises a sleeve body with the same section shape as the reinforced concrete column and a top plate fixedly arranged at the upper end of the sleeve body, and a pouring hole is formed in the middle of the top plate. One side wall surface, provided with the connecting plate, of the sleeve body is called as a first wall surface, and the other side wall surface opposite to the first wall surface is called as a second wall surface; and two ends of the opposite-pull screw rod respectively penetrate through the first wall surface and the second wall surface of the sleeve body.