Abstract: The normal current dissipation function can be affected by defects in the grounding electrode of the power transmission tower, impacting the safety of the power system and personal safety. Given that buried grounding grids are difficult to detect, this paper proposes a method for identifying grounding electrode defects in transmission towers using single-side dual-position excited ultrasonic Lamb waves. Geometric, ultrasonic excitation, and physical models are established, and the feasibility of ultrasonic guided wave detection is verified through simulation and experimentation. A single-sided dual-position defect identification method is proposed for on-site inspection, achieving defect localization by comparing guided wave signals at different excitation positions during actual inspections. Additionally, precise quantification of flat steel grounding electrode defects is achieved through feature extraction and neural network methods. Field test results show that, compared with commercial double-sided excitation transducers, the single-sided excitation transducer proposed in this paper has lower defect quantification error, reducing the average quantization error by approximately 76.2%.