Optical fiber leakage monitoring technology is internationally recognized as a promising solution for long-distance pipeline leakage monitoring. However, there is no clear effective monitoring scope for buried gas pipeline. In order to determine the effective monitoring range, the leakage simulation tests with different positions and different apertures are carried out on a 355 mm diameter pipeline with different nitrogen pressures. The test results show that the effective range of the fiber-optic temperature sensor is little affected by the size of the leakage aperture, but is greatly affected by the pressure and position, and is also affected by the soil compactness. In practical engineering application, the layout scheme of optical fiber temperature sensor can be adjusted according to the above factors to improve its monitoring effect.