The invention relates to a method of health status diagnosis, early warning and fault location for a protective layer of a buried metal pipeline, which comprises an accurate measurement method of a cathode protection potential of the buried metal pipeline, a reliable evaluation method of the transverse insulation resistance of the protective layer per unit length, a safety pre-warning and fault location method of the protective layer, and an implementation method of the micro power consumption of a measuring instrument. On the basis of the methods, the invention provides a quality evaluation method for the protective layer of the buried metal pipeline.