During cathodic protection commissioning and trial operation, the protection potential of about 20 km on both sides of the 3# valve chamber in the middle section of an ethane export transmission pipeline did not meet performance standard. In order to solve the abnormal phenomenon, the main influencing factors such as incorrect equipment debugging parameters, non-optimal setting of cathodic protection station and anode ground bed, stray current interference, poor quality of corrosion protection layer and abnormal leakage of protection current were analyzed and studied. It is preliminarily determined that the substandard protection potential is caused by abnormal leakage of current. The main causes of abnormal leakage of protection current, such as insulation joint failure or leakage, crossing casing lap, valve chamber leakage, etc., were analyzed. The abnormal leakage of valve chamber is identified. The surface area and current leakage of the ground electrode of the valve chamber in the main process area and the flare area are calculated, and the abnormal leakage is inferred to be the flare area. Checking the abnormal leakage parts of the pipeline and the grounding pole in the vent area, it is found that the self-tapping bolt of the insulation outer protection layer of the ground pipeline penetrates the corrosion protection layer and make contacts with the pipeline body, resulting in current leakage. Finally, rectification was carried out according to relevant standards and specifications, and the pipeline protection potential reached the standard requirement. The research results put forward systematic and comprehensive analysis and troubleshooting ideas and methods for the resolution of abnormal cathodic protection problems, and provide reference and suggestions for similar abnormal cathodic protection commissioning and trial operation in the future.