Abstract: The optical aberration difference between the biconvex Fresenl lens and the plane-convex Fresenl lens was investigated by designing a large aperture Fresenl lens. Generally, the Fresenl lens is used for collimation and its structure is planeconvex, but the analysis and comparison of the biconvex and the plane-convex Fresenl lenses with P-W method show that the biconvex Fresenl lens is better because of its specific imaging requirement. The two kinds of the Fresenl lenses were modeled in ZEMAX to validate the conclusion. However, it does not indicate that the biconvex Fresenl lens has advantages in all applications since it is application dependent. Therefore, Fresenl lenses should have different parameters for different applications.