Source and mask co-optimization is one of the most important resolution enhancement solutions in immersion lithography for nodes 45 nm and below. In order to reconstruct the optimum output pixelated source, a novel illumination mode conversion system design method based on a two-dimensional addressable micro-mirror array is proposed. The principle of reducing the number of micro-mirror required to reconstruct the source is analyzed, combing imaging and non-imaging optics, using cylindrical fly-eye lens to achieve the specific nonuniform intensity distribution on micro- mirror array. Based on this, optimization of each title angle of micro-mirror is programmed and the whole system is simulated. The results show the accuracy of the reconstructed source is less than 2.5 %, and pupil non-balance X,Y is below 0.5 %. The simulation results of reconstructed source with Prolith meets the design requirements. Compared with similar systems, the system ensures that the accuracy of reconstructed source with less than 4000 micro- mirror element, it′ s suitable for high integration of the next generation of immersion lithography system.