Abstract: The constitution and work principle of Microcor Internal Corrosion Monitoring System is introduced and the system is in-line used in the gas pipeline. The analysis on monitoring data obtained from the system and indirect monitoring data show that at 6 compressor stations, the level of internal corrosion is lower, harmful medium contented in the pipe is lower, the influence of corrosive gas on the pipeline is less and the internal pipe wall is protected well.