Objective To study the effects of HNO₃ concentration, spray pressure, mask gap and etching time on undercut . Methods Orthogonal experiment was designed to measure the undercut, meanwhile, analysis methods such as range analysis and analysis of variance were used to analyze the undercut, and the results were then verified using confirmatory experiment . Results It was found that the experiment conditions of the least undercut were a HNO₃ concentration of 0 . 3 mol / L, a spray pressure of 0 . 2 MPa, a mask gap of 50 μm and an etching time of 2 min. The undercut increased with the increase of the etching time, the spray pressure, and the mask gap, while it decreased with the rising concentration of HNO₃ . Conclusion Etching time has a significant effect on undercut . Other important influencing factors were spray pressure, followed by mask gap and HNO₃ concentration. Verification test showed that the optimal experiment scheme was feasible.