The invention discloses a distributed fiber disturbance sensor of a Sagnac interferometer and a disturbance positioning method thereof, comprising the following steps, using a Sagnac interferometer to couple an arm, synchronously adding a delayed fiber ring, namely superposing a delayed fiber ring in a single Sagnac interferometer to form two Sagnac interferometers with different length; realizing the time division multiplexing of the two Sagnac interferometers with different length by the propagation of optical pulses in the interferometer; and calculating the positions of disturbing points to realize the distributed sensing of the disturbance according to the amplitude of output signals of two Sagnac interferometers. The sensor has the advantages of low cost, simple structure and good stability.