A stereoscopic image printing device includes an actuating unit for moving a grating structure, and a positioning module. The positioning module includes a plurality of shelters, a planar light source for emitting light to pass through the grating structure and an interval between the adjacent shelters, and a photosensitive component for receiving the light passing through the grating structure and the interval between the adjacent shelters, so as to generate a corresponding optical intensity signal. The printing device further includes a controller coupled to the actuating unit and the photosensitive component for controlling the actuating unit to move the grating structure according to the optical intensity signal generated by the photosensitive component.