Aluminum electrolysis cells operate in complex environments influenced by the coupling effects of strong magnetic, electric, and thermal fields, making them prone to grounding faults that significantly affect both production efficiency and safety. Existing detection methods have limitations in precise fault localization and real-time diagnosis. To address these issues, a grounding fault diagnosis method based on excitation coupling is proposed. An alternating voltage signal with an amplitude of 30 V and a frequency of 100 Hz is injected at the front end of the aluminum electrolysis series. The dynamic response of the alternating voltage across the cell and its ground voltage is analyzed to examine the fault characteristics of the grounding system. It is found that, under normal operating conditions, the circuit exhibits capacitive characteristics, whereas, after a grounding fault occurs, the circuit′s characteristics transition from capacitive to resistive. A series of simulation experiments for both single-point and multi-point grounding faults are designed, introducing the capacitive-to-resistive ratio as a fault diagnosis indicator. By comparing the electrical characteristics of the system under normal and fault conditions, the following diagnostic criteria are proposed. When the alternating voltage across the cell exceeds a threshold, the phase difference between the alternating voltage across the cell and the ground voltage is less than 10°, and the capacitive-to-resistive ratio exceeds 104, a grounding fault can be confirmed. Experimental prototypes are established, and field evaluate have validated the effectiveness of the method. The proposed method is suitable for online monitoring and real-time diagnosis, offering significant improvements in both safety and economic efficiency in aluminum electrolysis cell operations. The results show that the method provides an efficient and reliable solution for grounding fault diagnosis in aluminum electrolysis cells.