To address the challenges in manufacturing ultrashort thin-film cavities, an ultrathin-film optical fiber temperature sensor based on a Fabry-Pérot interferometer (FPI) constructed using liquid adhesive is proposed. A miniature, high-sensitivity, and high-accuracy fiber-optic temperature sensor was developed and experimentally validated by optimizing the relationship between the material structure, film thickness, and cavity length. A structural model with an ultrashort Fabry-Pérot (FP) cavity length was successfully established. The experimental results reveal that the sensor has a temperature sensitivity of 342.05 pm/℃ and a linearity of 0.997 within the temperature range of 40-120 ℃. The sensor features a compact design, simple fabrication process, low production cost, and excellent temperature-response performance. It holds promise for applications in temperature detection within complex environments and manufacture of ultrashort FP thin films.