A transmission device for a 2D image display module includes rods in the box, a transmission element slidably mounted around the rods, a motor in the box and having a disk rotatably connected to a motor shaft, a driving rod eccentrically formed on top of the disk and a driving board provided with a slot defined to receive therein the driving rod, wherein distal ends of the transmission element are securely connected to the driving board, and a securing member securely connected to the transmission element to be adapted to connect to either the backboard or the lens. Rotation of the driving rod is able to drive the driving board to move, which drives the lens to move opposite to the driving board so that the image is revealed as a result of relative movement between the backboard and the lens.