The invention discloses a steel tube tower and pole number plate hanging device, which comprises a number plate bracket and a mounting bracket, wherein the number plate bracket comprises a fixing endfor fixing a number plate and a mounting end which is fixedly connected to the mounting bracket; a lower clamping strip, which is fixed, is arranged at the bottom of the fixing end; an upper clampingstrip, which can move up and down relative to the lower clamping strip, is arranged at the top of the fixing end; a sliding block is arranged on the lower clamping strip; an upper gear and a lower gear, which is in meshed transmission with the upper gear, are arranged on the upper clamping strip; a fixed gear rack, which is matched with the lower gear, is arranged on the lower clamping strip; a rotary rod, which can drive the upper gear to rotate, is arranged on the sliding block; an upper sliding groove is kept in the bottom of the upper clamping strip; and a lock pin, by which the upper gearand the lower gear are separated from meshing, is arranged in the upper sliding groove. The invention aims at providing the steel tube tower and pole number plate hanging device which is simple and convenient in mounting process and is adaptive to number plates differing in size.