A reflective optical fiber temperature sensor is highly developed on the basis of the temperature-dependent character of ZnO thin film′s optical absorption spectra. ZnO thin film as sensing material is deposited on a sapphire triangular prism surface by the electron-beam evaporation technique. And then the triangular prism and a fiber-ending located at a convex lens′ focus are employed in the mode of a reflective optical configuration. According to the measurement results, the goodness-of-fit of the sensor′s temperature curve is above 99.3%, and the sensitivity of the sensor is beyond 0.05 nm/℃ when the temperature varies from 300 K to 773 K. Moreover, this temperature sensor is steady enough for a wide temperature range measurement in the experiment, even from 10 K to 1000 K.