We proposed a temperature sensor of tapered multimode fiber based on surface graphene modification (SG-TMMF) in this paper. Specifically, a section of TMMF is fused between two sections of single-mode fibers (SMF), and then its surface is coated with a graphene film by the liquid phase transfer method. Graphene interacts with the optical field of the TMMF. The effective refractive index of the SG-TMMF composite waveguide changes with the external temperature. As a result, its optical transmission loss varies, achieving temperature sensing. The experimental results show that graphene can effectively improve the temperature sensing capability of TMMF. In the range of 20-90 ℃, the SG-TMMF with a waist diameter of 9.95 μm has a loss sensitivity up to 0.1589 dB/℃ and a linearity of 0.984. Besides, its sensor has good reversibility. The proposed sensor demonstrating simple manufacturing and high sensitivity has a good application prospect in scientific research and temperature measurement areas in industrial and agricultural production.