To improve the accuracy and speed of the online temperature measurement system for power cables, a method for fitting data reference points was proposed, which uses fiber interleaver filter to replace referencegrating. Least square method is utilized to fit linear dependency between bragg wavelength of fiber grating and tuning voltage of FabryPerot filter. With wavelength shift that is demodulated by the tunable FabryPerot filter, the system realizes temperature measurement of power cables. The result of the research shows that fiber interleaver filter can replace the referencegratings in thermostatic environment to calibrate the wavelength shift. Error of reflected wavelength is ±5pm, and mean square error of temperature is 0.7℃.