This paper studies the application of interference caused by mode coupling in a tapered multicore fiber to temperature sensing. A weakly coupled multicore fiber becomes a strongly coupled multicore fiber after being tapered and has characteristics of supermode interference. A weakly coupled seven-core fiber is fused into a single-mode fiber after being pulled back and forth by a hydrogen flame at a uniform speed. When the diameter of the optical fiber decreases and distance between cores is reduced to a certain extent, supermode interference occurs, thus temperature sensor with simple structure, high sensitivity, and strong specificity is fabricated. It is determined that the smaller the fiber diameter and the longer the taper length, the stronger the mode coupling. A tapered multicore fiber with a cone length of 1.8 μm and a cone diameter of 31.36 μm was selected. The sensitivity of the designed temperature sensor reaches 840 pm/°C, which is 52.7 times higher than the previously reported value.