A method of fiber Bragg grating (FBG) wavelength detection based on an all fiber Mach-Zehnder edge filter is proposed. Each output port of the edge filter shows comb-like transmission characteristics, and its spectrum is opposite to the other port. Wavelength message of FBG sensors is transformed into power message by a pair of the filtering edges of the filter. The wavelength measurement range and resolution are tunable in fabrication by adjusting the length difference of the two interference arms of the filter. And the affection of power variation of the system can be eliminated through two types of comparing calculation. FBG temperature sensing with this wavelength detection method gives a wavelength accuracy of about ±10 pm.