For the reduced-magnification optical projection system in high precision digital lithography, a kind of digital lithography projection lens, composed of six lenses and suitable for 0.7XGA Digital Micro-mirror Device (DMD), is developed and designed. Through optimizing and splicing the three pieces of lens’ structure, the objective lens, of which numerical aperture NA=0.1, magnification -0.255 8 and resolution 3.5 μm, is obtained. The results of Zemax software show that it reaches the diffraction limit, which is not affected by DMD grid effect. The optical path difference is less than λ/5 and MTF is more than 0.58 at 145 cycles/mm, which shows that it meets the requirement of the lithography lens’ design. Utilizing Monte Carlo method to analyze the tolerance, 100 groups of lenses’ assembling and fabricating are simulated. The result indicates 90% of the lenses’ FMTF>0.55 when setting the space frequency to 145 cycles/mm, which verifies the practicability of lenses’ assembling and fabricating.