Abstract: CP performance and service life of pipeline are directly affected by the coating quality of oil pipeline. The statistical analysis on the variation of leak detection coating data and/or CP parameters is made for the Lu-Ning oil pipeline, which has been operating safely up to 17 years since its commissioning. Detailed objective and scientific analysis and verification are made on the coating quality based on the insulating resistivity of the coating detected and internal inspections as well as bell-hole inspections made. It is concluded that the coating quality of the line is deteriorated obviously and has to be recoated. It is pointed out that only by recoating 30-40 km per year can the recoating period for the whole line be guaranteed.