Abstract: The present disclosure discloses a heat transfer printing on-line code printing system. A conveyor belt is arranged on a worktable. A pressing conveyor and a code printer are erected on the worktable. The pressing conveyor includes a mounting frame. An adjustment frame located above the conveyor belt is arranged on the mounting frame. Two roller groups that are arranged opposite to each other are rotatably arranged on the inner side of the adjustment frame. Acting sides of the two roller groups penetrate out from the bottom of the adjustment frame to the position above of the conveyor belt. The two roller groups are in coaxial transmission. The adjustment frame is connected to the mounting frame, and the mounting frame is in threaded connection with an adjustment rod. The inner side of the mounting frame is connected with multiple support components that are elastically pressed against the adjustment frame.