In response to the requirements for robustness and high measurement sensitivity of temperature sensors in industrial production, a temperature sensor based on a cascaded dual-fiber-ring structure (Dual-Fiber-Ring Tandem Sensor, CDFRS) is proposed in this paper. The sensor is formed by knotting ordinary single mode fiber (SMF) into two cascaded fiber rings of different diameters, and encapsulated in polydimethylsiloxane (PDMS) with low Young's modulus. The proposed sensor is based on the whispering-gallery mode theory. The whispering-gallery mode resonance effect is enhanced through the cascaded dual-fiber-ring structure, and thus the sensitivity of the sensor is improved. The experimental results show that within the temperature range of 25–30 °C, the temperature sensitivity of the CDFRS reaches -1.0853 nm/°C, the linear fitting coefficient is 0.9939, the temperature resolution is 0.0461 °C, and the standard deviation in repeatability experiments is approximately 0.056 nm/°C. The CDFRS proposed in this work is characterized by simple fabrication, rapid response, and high sensitivity, and is applicable to scenarios such as flexible sensing, wearable devices, and intelligent machinery monitoring.