The application discloses a method and apparatus for monitoring a tunnel. The method comprises the steps of acquiring a target defect type which is the defect type of original data acquired by a tunnel monitoring system; searching for a target processing scheme corresponding to the target defect type from a preset file which is stored with defect types, processing schemes and corresponding relations thereof; and operating the tunnel monitoring system correspondingly based on the target processing scheme. The application solves the technical problem of failure to modify the tunnel monitoring system timely by taking appropriate measures based on the type of a defect.