By introducing PCM in the multifrequency principles and using DM produced by Radiodetection company, the article showed respectively the detection results of the anticorrosion layers from Shuwulian to first station, from Shuyilian to Shuwulian and from Shusilian to first station gathering pipelines in Shuguang oil production plant in Liaohe oilfield. The inferior and poor level of the three pipelines was accounted for 50.2%,51.8% and 42.9% respectively on all the anticorrosion layers. The detect results and the verification of suspected leaks were consistent. There were certain limitations when PCM was used only to detect underground pipes .If it was combinated with other detection means, the results would be more accurate.