A steel wire transmission system includes plural slide rail seats, plural slide rails, plural wheel sets corresponding to the plural slide rails, plural slide blocks, plural steel wires, plural guide rods and a printhead module. The plural slide rails are disposed on the corresponding slide rail seats. Each wheel set includes a driving wheel and a driven wheel corresponding to the driving wheel. The driving wheel and the driven wheel of each wheel set are fixed at two ends of the corresponding slide rail. Each slide block is sheathed around the corresponding slide rail and movable between the corresponding driving wheel and the corresponding driven wheel. The plural steel wires are wound around the corresponding wheel sets. Each guide rod is connected with two corresponding slide blocks. The printhead module is connected with the plural guide rods.