It is very important to detect the fiber Bragg grating(FBG) wavelength accurately for engineering monitoring in bad environment. This paper reviews the methods of improving wavelength demodulation accuracy and wavelength signal processing in different demodulation systems. It mainly introduces the research progress of demodulation system based on tunable laser, tunable filter and spectrometer to improve wavelength calibration accuracy, analyzes the influence of the algorithm in the process of signal demodulation on the demodulation performance of FBG sensor.