As a result of the big difference in the required space between automation machine vision system and assembly line, the traditional fixed-focus lens cannot meet the practical requirements. There is a need for the big span working distance of optical imaging system. Based on the influence of changes in the object surface position on the primary aberration, with multiple structure function of Zemax software, the wide working distance lens is designed. The results show that the focusing range is from 146 mm to infinity, and the maximum aperture is F2.8. At the center field-of-view (FOV), the modulation transfet function (MTF) is greater than 0.3 at the spatial frequency of 100 lp/mm and the MTF at the 0.7 FOV is greater than 0.3 at the spatial frequency of 72 lp/mm. Such a system can replace the manual work to observe the whole assembly line and thus can improve the degree of automation.