For the requirement of large area graphic exposure of digital projection photolithography, a graphic matching method is proposed based on grayscale mask modulation, which includes graphic segment, mask design, sub-graphic grayscale modulation and sub-graphic exposure. Before graphic inscription, the exposure graphics are segmented into many sub-graphics of size 1024 pixel×768 pixel, then every sub-graphic is multiplied by corresponding mask for the realization of exposure graphics′ pretreatment. Feasible edge grayscale masks are designed according to the principle of digital micromirror device (DMD) modulation for grayscale graphic. The basic method of graphic segment and principle of masks design are given in this paper. The computer simulation experiment shows the process of graphics matching. The results show that matching problems in large area graphic inscription can be solved properly using this method. Besides, the quality of graphic inscription using this method is effectively improved.