A three-parameter sensor of fiber micro-cavity based on the cavity ring down s pectroscopy (CRDS) technology is proposed and implemented.The micro-cavity on single mode 1060nm fibers is achieved by direct writing with high frequency CO_2laser pulses.As a sensor unit,the fiber micro-cavity is accessed to the fiber loop resonator.The temperature,the refractive index and the strain are measured at the same time by measuring the ring down time of the pulsed laser. Based on the analysis of optical time domain multiplexing (OTDM) principle and t he system configuration,a phase modulation is introduced in different optical ring down c avities.Three optical ring down cavities with fiber micro-cavity are connected in parallel,an d a common light source and a detector are provided.Therefore,the sensing results of different pa rameters are output in time sequence,and the detection of three parameters is real ized at the same time.This sensor structure is reasonable,the maneuverability is strong,the later data processin g is simple,and the experimental results are repetitive very well.On this basis,we can extend th e sensor structure to the four-parameter sensor.The multi-parameter sensor sys tem can be realized even more.