The contents and methods of pipeline external corrosion detection were introduced. Corrosion condition detection and data analysis were conducted in detail for pipeline leakage which occurred many times. The results show that pitting corrosion happened and eventually leads to corrosion perforation. The main reasons of the pipeline corrosion are anticorrosive coating damage, soil corrosion and polarization potential do not reach protection potential of pitting corrosion. According to the analysis, a series of anti corrosion suggestions are given.