By using the reflectivity property of fiber Bragg grating (FBG) and the coupling property of coupler, a wavelength-division demultiplexer based on FBG coupler is designed. The WDM signals are injected from the input port of the coupler, and the signal which has the same wavelength as that of FBG will be output from the demultiplex port of the coupler, and the other signals will be output from the output port of the coupler, thus the demultiplex is implemented. The experiment of two signals with different wavelengths of 1554.248 nm and 1555.859 nm are implemented, and the extinction ration of each is 57 dB, and the center wavelength of FBG is 1555.86 nm. The results show that the signal output from the demultiplex port with extinction ration of 48 dB.