The all-fiber delayed self-hetrodyene interferometer(FDSHI) system with 3 km optical path difference is established based on the principle of Mach-Zehnder interferometer(MZI).The output transient characteristics,including the output wavelength and linewidth,of the 1 582 nm distributed feedback(DFB) laser diode(LD) under temperature modulation are measured.The results indicate that the output wavelength of the DFB LD varies with temperature linearly.Through Lorentzian fitting for the optical current power spectral density function,we achieve that the LD linewidth is 3.24 MHz which is close to the theoretical value of 3 MHz.