In order to monitor the fiber-optic links in Tibet, which are sparsely populated and have long transmission distances. This paper presents a method of improving the spatial resolution and measuring the distance of a Linear Frequency Modulated (LFM) Optical Time Domain Reflectometry (OTDR). The method achieves high spatial resolution and large detection distance by generating an intensity modulated analog chirp signal with a frequency range of 200 MHz and a pulse width of 20 μs. Experiments are carried out on the actual fiber-optic transmission link in Tibet using this method. The experiment results show that the method can achieve a spatial resolution of 0.000 53 km on a fiber link with a length of 240 km. And compared with the single pulse OTDR with the same measurement parameters, the dynamic range is improved by 8.5 dB.