At present, there are many kinds of gas pipeline leak detection methods at home and abroad. In this paper, combined with the actuality of pipeline in China and the experience of international practice of detection methods and computer automation instrumentations, real-time leak monitoring model of the long distance natural gas pipeline was researched. In order to adapt to the needs of simulation, under strictly meeting the stability requirements of the characteristic line, the premise of the grid layout in the form of the characteristic line was changed, and the solution of transformed equations was given. Leakage point and the amount of leakage were determined. And the mathematical model of leak detection used in this chapter is also applicable to the judge and positioning in the pipeline blockage accident.