A cascaded double-cavity temperature sensor based on hollow fibers encapsulated by polydimethylsiloxane (PDMS) membrane is proposed and prepared. The sensor consists of an air cavity (FP1) and a PDMS cavity (FP2) that are cascaded, and the PDMS cavity is much shorter than the air cavity so that the sensor can meet the condition of the Vernier effect [the optical path of FP1 is close to that of the composite cavity FP3 (composed of FP1 and FP2)]. When the external temperature changes, the PDMS membrane expand to both sides, resulting in the interference spectra of FP1 and FP3 move in the opposite direction. The experimental results show that the interference spectrum of FP1 and FP3 manifest the Vernier effect, and the envelope of the interference spectrum is obvious. The temperature sensitivity reaches 1.32 nm/℃ in the range of 50--60 ℃, which is consistent with the theoretical analysis results. The proposed sensor, with the advantages of small size, light structure, high sensitivity, and simple preparation, has application potential in chemistry, biology, and medical treatment.