The invention discloses a distributed optical fiber sensor. The sensor comprises a light source module, more than one optical fiber ring-down cavities and a connection component. The light source module is formed by a tunable laser, an acoustic-optical modulator and a radio frequency modulator. Each optical fiber ring-down cavity is formed by an optical fiber ring and a fiber bragg grating sensingunit. The optical fiber ring at least comprises an optical fiber coupler, an erbium-doped optical fiber amplifier and an optical fiber circulator which are connected by an optical fiber. The connection component connects the output end of the acoustic-optical modulator and the first port of the optical fiber coupler. The third port of the optical fiber coupler is connected to the input end of a photoelectric detector. The output end of the photoelectric detector is connected to a signal processing and display system via a high speed data collection card. The synchronous trigger port of the high speed data collection card is connected to the second output port of the radio frequency modulator. The connection component comprises one single mode fiber and one multimode fiber. In the invention, disadvantages in the prior art can be improved and the detection precision of a temperature and a dependent variable is increased.