Abstract: In order to study the zooming for large-area laser projection lithography, using Zemax optical design software, the defocusing effect on modulation transfer function (MTF) and optical path difference (OPD) was simulated, the effect of OPD and MTF on the imaging quality of projection imaging lithography was analyzed, and the maximum defocusing range of the system was also provided. A zooming method by using microscope was proposed, the zooming errors of this method was mainly come from the depth of field of microscope. According to the expression of the depth of field and the maximum defocusing value of this system, a microscope whose depth of field was not more than the maximum defocusing amount was chosen to construct the zooming system. The experiment was demonstrated based on the zooming system for lithography. Experiment results illustrate that the new zooming method for project imaging lithography can obtain a good lithography image quality.