Abstract: In order to carry out an overall diagnousis and analysis on the abnormal state in the gas drainage pipeline network, the gas pressure drop equation based on the compressible gas flow theory was established and the method by using the descending curve slope of the pipeline pressure square (PPS) for evaluating the leakage and blockage status of the gas drainage pipeline network was proposed. The effectiveness and reliability of the proposed method were verified through the laboratory simulation test and field test. The results showed that the descending curve slope of the pipeline pressure square was invariant for the same gas drainage pipeline network under the normal running state; when the leakage or blockage happened in the middle pipe section, the descending slope of the pressure square of this pipe section would quickly decreased, and under the blockage state, the descending curve slope of the pressure square of the downstream pipe section would return to the consistent with that of the upstream pipe section, when the leakage happened in the pipeline, the descending curve slope of the pressure square of the downstream pipe section would less than that of the upstream pipe section.