To meet the illumination system requirements of 45 nm and below node lithography technology, the micromirror array (MMA) used in the beam shaping unit of deep ultraviolet lithography illumination system is used as the key device to produce the freeform source required by the source-mask optimization(SMO) technology. Based on the structural parameters of MMA as well as the manufacture and adjustment characteristics, the angle error types of MMA are analyzed. On this basis, the Monte-Carlo tolerance analysis method is used to simulate the actual manufacture and adjustment processes. After the influence of the micromirror angle error on the exposure results is investigated, the angle tolerance that meets the exposure requirements is established. The results show that when the angle adjustment tolerance and the process angle tolerance of MMA in the orthogonal direction are within the scope of (±0.04°, ±0.06°) and (±0.04°, ±0.04°), respectively, the critical dimension error (CDE) obtained by exposure is less than 0.33 nm at a confidence probability of 98.1%.