It is a crucial problem how to produce two pictures for left-eye and right-eye respectively with proper horizontal position disparity in autotereoscopic 3D display. The theoretic interrelation between the left-viewpoint and right-viewpoint in the model space by Direct 3D and the horizontal position disparity in the display screen has been established in this paper. The method for getting proper horizontal position disparity has been put forward aiming to provide proper sensation of depth as in real world and the most comfortable vision

and the theoretic formula is presented as well. Furthermore

two parameters

the position of left-viewpoint and fight-viewpoint in model world and the movement of the perspective plane

have been given in this paper

which directly affects the view result

The conclusions from this paper have gone into application and marvelous auto-stereoscopic 3D view has been achieved