In recent years, DMD-based maskless lithography, as a tool for IC mask and microstructure fabrication, has attracted wide attention. It employs a computer-controlled DMD as a switchable projection mask and binary pulse-width modulation to generate grayscale. However, the surfaces of the imaging objects will deviate from the designed and produce ruled surges when the tool is used for fabricating microstructures with continuous surface relief. The physical mechanism of the surges was firstly explored, and then simulated annealing algorithm was adopted for removing surface surges. The simulation results show that the imaging quality after optimization is clearly better than that before optimization and the surges were mostly removed in the 5% range of relative exposure deviation. Finally, the axicon lens array with good surface quality was fabricated by using the optimized mask. The method is simple and provides a new way to improve the imaging quality in DMD-based maskless lithography, which is very useful for the fabrication of high-performance microstructure device.