Abstract: A graded-index multimode fiber (GI-MMF) with reduced core size was designed and fabricated with large effective mode area and low intermodal dispersion for Raman distribution temperature sensor (RDTS) to simultaneously achieve high spatial and temperature resolution. In experiment, the temperature and spatial resolution of the RDTS was measured using different types of fibers under different launch conditions based on a commercially available RDTS system. By using the GI-MMF under the overfilled launch condition, a 1℃ temperature resolution was achieved with a spatial resolution degradation of 0.13 m at the distance of 25 km. The spatial resolution degradation using the standard MMF is 1.58 m in comparison. Moreover, the RDTS using the proposed GI-MMF under the single mode launch condition achieved a temperature resolution of 4.7℃ temperature resolution at the distance of 25 km with a 2.2℃ improvement and no degradation on spatial resolution compared with that using the standard SMF.