The key issue during the implementation of the large size autostereoscopic 3D LED display system based on holographic lens is the high-precision stitching and assembly of the holographic lens sheets. Theoretical calculation and expriment results show that, if the horizontal relative position error of the holographic lens and the led module is less than 1.332mm, the 3D display effect of the autostereoscopic 3D LED display will be good enough. According to the projection fringes of the autostereoscopic 3D system, the real-time adjustment method of the lens position is investigated and introduced. On the basis of this method, an image processing method suitable for the precision stitching is proposed and a LabView program of the image processing method is written. The experimental results show that the precision of distance of the light fringes is less than 0.1mm, which indicates that the position error between the holographic lens sheets and the LED panel is less than 0.03mm. The method satisfies the requirement of on-line stitching of the holographic lens sheets in autostereoscopic LED display system, it can be used as precision on-line stitching method of holographic lens panel.