To increase the uniformity of image illumination of wide-viewing-field optical systems, influencing factors are analyzed theoretically. Idea of optimizing image illumination uniformity by contrast of axial rays′ section area and oblique rays′ section area is raised. Mathematic model is established in ideal optical system. The law that ratio of rays section area changed with viewing-field angle influenced by central circular obscurations is acquired. Degeneration of modulation transfer function (MTF) caused by obscuration is analyzed. Optimization approach through dynamic data exchange (DDE) between software Zemax and Matlab is put forward. A focal length 56 mm, relative oparture 1/5.6, 2ω=80°air-survey camera lens is taken as an example to perform the optimization, and result shows its non-uniformity of image illumination decrease to 3.5% from 22.3% by adding a central obscuration on fifth surface, whose outer radius is 4.384 mm. The change of MTF is discussed in this example, and the MTF values with obscuration can satisfy the CCD imaging requirements.