A high power pulsed laser diode is used to pump a 1 km GI multimode optical fiber in which the ratio of core to cladding is 50/125 μm. Meanwhile, the OTDR (Optical Time Domain Refiectometry) technique and high speed sample average technique are adopted to measure and analyse spectra from backseattering fibers. The study of the temperature character of anti-stokes SCattering, the intensity of which is only 10-8～10-9 of the incident light, and its aPPlication in the distributed optical fiber temperature sensors are emphasized.