In order to collect images effectively with a corneal topography based on the Placido disk, a system with a symmetrical achromatic lens and a collimating illumination lens is designed according to characteristics of human corneal and CCD plane array parameters. The initial structure of the imaging lens is calculated based on the theory of primary aberration and the PW method. The collimating illumination lens parameters is designed by paraxial ray trace equations. The imaging system is optimized with the Zemax software. The imaging lens structure is composed of four lenses in two groups, its effective focal length is 20 mm, back working distance is 19.2 mm, full field of view is 8°, relative aperture is 1/3, and maximum optical total track is 20 mm. The modulation transfer function in all fields is larger than 0.3 at resolution of 66 lp·mm－1 and the full field-of-view distortion is less than 0.5%. The system is characterized by its simplicity, compactness, easy processing, low cost and high imaging quality, which meets the requirements of the whole system very well.