Abstract: According to the requirement of automatic focusing in HUD parallax measuring principles, an inner focusing objective of larger relative aperture and focusing range was designed. In order to eliminate the defects in traditional design, the selected lens groups are assembled into a system and multiconfiguration method is adopted to optimize the length of different object distance. In this way, the problem of uncontrollability of short-distance imaging quality was solved. The newly designed inner focusing lens performed well and stable under different object distance, MTF values are above 0.4 both on the optical axis and off-axis in infinite distance when the spatial frequency is 120lp/mm, 0.3 on the optical axis at 300mm; the off-axial sagittal of arc is 0.3 and meridian is 0.2, and the relative distortion is confined within 1%. All achieved makes the after-treatment of the image more convenient.