In the test of electrostatic discharge (ESD) capacity, a special digital circuit for multi-power domain failed at 1 700 V of the human body model (HBM). The failure position after electrostatic test was located by the HBM test and the optical beam induced resistance change (OBIRCH) failure analysis. According to the failure analysis results and theoretical analysis, the reason was due to weak reverse electrostatic capacity of the electrostatic diode. The transistors were used to replace the electrostatic diodes, and the interior of OUT2 port was optimized for electrostatic layout design. After the revision, the ESD protection capability of the circuit reached more than 2 500 V. The results of this study had reference value for ESD failure analysis and robustness improvement of multi-power supply domain digital circuits.