Internal corrosion of oil and gas pipeline is one of the main factors leading to pipeline failure. Based on principle of the fiber Bragg grating strain sensor as well as the multiplexing technology, an on-line monitoring system based on optical fiber grating sensors is studied. The corrosion degree of the inner pipeline can be determined by the surface stress changes, and array sensor network using 7 channels of FBG sensor is set up in the monitoring system, through temperature compensation grating to realize temperature compensation. Experiments show that the system pressure measuring accuracy is high, with the system error less than 2.23%. The feasibility and stability of the system are validated by comparing the measurement results with the actual pressure from the scene of the production, meeting the requirements of internal corrosion online monitoring.