Currently, a broad series of methods to obtain photoluminescent (PL) carbon dots (CDs) have been developed. CDs are novel fluorescent materials with the advantages of easy chemical modifications, chemical stability, biocompatibility as well as low toxicity. As a result, nanocomposites based on CDs have great potential for functional applications. In this paper, poly(N-isopropylacrylamide) (PNIPAM)/CDs composites have been used as a temperature sensor. The detection signal is luminescence which possesses high sensitivity, improved facility and provides the possibility for visual detection. With the temperature increasing, the fluorescence intensity of the composites decreased sharply at around 32 °C with the existence of PNIPAM. The composites show perfect reversibility after 12 heating and cooling processes. Moreover, compared with CDs, the CD composites also show good UV resistance at high power UV exposure.