The scanning exposure patterns by Digital Micro-mirror Device(DMD) array in some directions have a saw-tooth edge of one pixel, to solve this problem a free surface optical lens is designed and installed at 1 mm distance of DMD window glass. The imaging of the microscopy array has a linear dislocation which caused by free surface optical lens. When the original line width and photolithography efficiency are invariable, the edges of the exposure pattern are smoothed. The linear dislocation form is analyzed theoretically. Based on the mapping principle, the initial data of the free surface is calculated by Matlab. The model of the ideal lens shape is constructed and optimized by Zemax. And the exposure effect with and without the lens is simulated. The results show that within the tolerance range of 2 μm, the dash saw-tooth edge of the exposure pattern is reduced from 0.14 pixel to 0~0.01 pixel, the slash edge of the saw-tooth is reduced from 0.338 to 0.110~0.125 pixel, and the change of the line length and width range respectively from －0.153 to 0.05 pixel, and from －0.058 to 0.153 pixel, when the energy decreases to 0.9 times of the original after installing the lens. The deformation range of the pixels and scribe line meets the manufacture precision of PCB which is about 10~30 μm. The proposed method has the advantage of reducing exposure energy demand and light source cost.