A single-mode-few-mode-thin-core-single-mode (SFTS) structure based optical fiber sensor is fabricated and experi-mentally studied. The sensing principle relies on the inter-modal interference. Since the core diameter of few-mode fi-ber (FMF) is larger than that of single-mode fiber (SMF), the FMF helps to allow more light to enter the cladding of thin-core fiber (TCF), which helps TCF to excite cladding modes. The interference between core and cladding modes in TCF occurs at the joint of lead-out SMF and TCF. Experimental results demonstrate a refractive index (RI) sensitiv-ity of .103.34 nm/RIU and a temperature sensitivity of 0.05 nm/℃. The proposed sensor not only can measure tem-perature, but also can measure RI. In addition, the proposed sensor is simple for without complicated fabrication proc-ess.