An auto grid moving apparatus for an X ray imaging device is provided. The apparatus includes: a grid; a grid holder on which the grid is disposed; a fixing base; and a double sided timing belt geared with at least two timing wheels at the two ends of the timing belt on the inner side face of the timing belt and geared with the grid holder at the outer side face of the timing belt, wherein one of the timing wheels has a motor disposed thereon, the motor being configured to drive the timing wheel to move the timing belt and to drive the grid holder to move.