A temperature sensor of fiber micro-cavity based on the cavity ring-down spectroscopy (CRDS) technology is proposed and implemented. The micro-cavity on single mode 1060 nm fibers is achieved by direct writing with high-frequency CO2 laser pulses. As a sensor unit, the fiber micro-cavity is accessed to the fiber-loop resonator. Temperature sensing is realized by measuring the ring-down time of the pulsed laser. In the temperature range of 24 ℃~93 ℃, the sensitivity of the temperature sensor is up to 83.36 ns/℃. Experimental results show good linearity.