In order to meet the needs of the backing-up lens in cars, a wide-angle lens has been designed. The lens has four elements, the first is a piece of optical glass, the other 3 elements are plastic, and the lens is able to work under bad conditions. The lens has an F number of 2.8, the horizontal field is 185 degrees, and the test showes that the off-axial distortion is corrected perfectly. Mass production of the lens has begun.