The invention discloses a steel structure fastener capable of realizing firm connection. The steel structure fastener comprises two fixing plates, first inserting rods are fixed to the faces, close to the inner sides, of the two fixing plates, the first inserting rods are arranged at the two ends of the same side face of the fixing plates, the bottoms of the first inserting rods are each of a two-half structure, the two fixing plates are fixed through bolts, protruding blocks are arranged at the bottoms of the fixing plates, the fixing plates are connected to the two sides of a steel structure in an inserted mode through the first inserting rods, the steel structure is provided with first pin holes matched with the first inserting rods, circular truncated cone grooves are formed in the bottoms of the first pin holes, and tip cones are placed in placement grooves. When the steel structure fastener is mounted, through the arranged first inserting rods and the formed first pin holes, first locking blocks slidably arranged at the bottoms of the first inserting rods are jacked up by the tip cones to slide towards the two sides, the first inserting rods and the first pin holes are locked and not separated, mounting is firm and reliable, and automatic locking is achieved so that separation can be avoided.