The excimer laser beam is needed to be expanded in one dimension to meet the requirement of square cross-section distribution for beam shaping unit, because of the rectangular cross-section distribution characteristic of laser source for projected lithography which holds 90 nm exposure linewidth. The reported beam expanding units have the deficiencies of serious speckle effect of coherence and the strict tolerance to alignment. A kind of multi-component parallel reflective expander is proposed aiming at the shortages above. The structures of such beam expanding units are determined by calculating linear equation set. One of the structures, which is called four-component beam expanding unit, has only one transmissivity to reduce the cost of coating. A synthesis comparison is executed at the aspects of tolerance analysis, transmission efficiencies and uniformities of output beam. According to the simulation results, the designed four-component beam expanding unit is proven to be an optimal scheme by the evident reduction in speckle effect and tolerance sensitivity. Meanwhile, the homogeneity of output beam is improved, which is favorable to enhance the uniformity of the whole illumination system.