For the 1:1 laser projection lithography system used to achieve large-area patterning with higher resolutions as well as higher throughput, the key parameters such as the laser beam geometry, the numerical aperture of projection lens, the laser source power and the pulse repetition rate are theoretically analyzed. It is expounded the process of uniform exposure in hexagonal beam shape, the advantages and limitations of 1:1 projection owing to numerical apertures deciding the resolution, as well as the cause of choosing larger laser power and pulse repetition rate. Meanwhile, the projection lens for a unit-magnification, refractive imaging system is tentatively simulationdesigned using ZEMAX optical design software. The optimized three-dimensional layout is plotted. For the designed results, the maximum optical path difference is smaller thanλ /4 within entire visual field. The resolution for feature sizes 10μm can be achieved within depth of focus 400μm by evaluating MTF. The maximum field curvature is within 10μm and the maximum distortion is small than 0.000007%. This fulfills the demands in technical specifications.