Top-Gaussian illumination generation technology has considerable application prospects in photolithography. We propose a detailed design and optimization method for the optical component that generates the top-Gaussian illumination field. This method can generate a field with a specific profile in the scan direction and a rectangular distribution in the nonscan direction. The energy density is reduced by jointly designing the first and second microlens arrays (MLAs). Thus, design freedom becomes more extensive. The requirements of the illumination field are met by the designed top-Gaussian illumination field, whose dimensions in the scan and nonscan directions are insensitive to illumination mode. Furthermore, the influences of the rectangular distribution dimension and the Gaussian distribution σ errors on the dimension of the top-Gaussian distribution are studied. The design results show that the maximum energy density in the second MLA can be reduced to 17.43% of that in the general design method. The analysis results indicate that the full-width-at-half-maximum error of the rectangular illumination field in the scan direction should be restricted within ±0.3  mm, and the σ error of the Gaussian distribution should be restricted within ±0.05  deg. The proposed method should increase the service life of the key component of the photolithography machine, and the cost of the manufacture and maintenance may be decreased.