Square tube connecting device

The utility model relates to a square tube connecting device which solves the technical problem that in the prior art, a connecting device needs to be provided with a through hole in a square tube, and the strength of the square tube is damaged. The device comprises two first sleeve connection square pipes, a second sleeve connection square pipe and a threaded rod, the upper bottom wall and the lower bottom wall of each first sleeve connection square pipe are connected with connecting plates provided with penetrating holes, the front side wall and the rear side wall of each first sleeve connection square pipe are provided with threaded through holes, and the threaded through holes are in threaded connection with fastening bolts; a connecting sleeve is arranged on the second sleeving square pipe, and an inner hole of the connecting sleeve is coaxial with the through hole in the corresponding connecting plate; external threads are arranged at the two ends of the connecting rod, the connecting rod is coaxial wit