The cutting characteristics of the polymer determine the processing quality of the microstructure. Considering photoresist SU8 as the representative polymer in this research， the cutting characteristics of the photoresist mask were studied through experimental analysis and simulations. The stress-strain relationship of SU8 was analyzed via the nanoindentation method， and a cutting simulation model of SU8 based on the energy method was established. Next， the cutting characteristics of SU8 under different cutting parameters were simulated using AdvantEdge FEM. Finally， an experiment involving ultra-precision machining of SU8 was performed. According to the simulation and test results， the effects of the cutting parameters and tool rake angle on the surface quality were analyzed， and the cutting parameters of SU8 were optimized. The results demonstrat that the surface roughness decreases with an increase in the cutting speed and increases with the feed rate and depth of cut. Within the scope of the experimental conditions， when the cutting speed is 2.09 m/s， the feed speed is 1 mm/min， the depth of cut is 2 μm， and the tool rake angle is 0°； the surface roughness R_a of the photoresist reaches the optimum value of 7.4 nm， and there are no microfractures. Finally， according to the test and simulation results， the processing parameters were optimized， and a microlens array mask structure was fabricated on SU8 with high precision.