Abstract: The interference condition of the buried steel pipeline of the Pearl River Branch Pipeline was evaluated by the on site AC and DC interference parameters test. The results showed that the pipeline was subject to serious AC and DC mixed interference. Using AC voltage parameters and AC current density parameters to evaluate the interference of the pipeline, we would get completely different evaluation conclusions. Cathodic polarization caused by cathodic protection had obvious influence on localized resistivity around the damage point of anti-corrosion coating. Under low resistivity and high polarization condition, the AC voltage of the pipeline might be very low but the AC current density might be very high.