To increase the numbers of multiplexed gratings on a fiber of fiber Bragg grating(FBG) multiplexed sensing demodulation technique,a demodulation scheme to detect the wavelength shift,which is based on F-P tunable filter and uses the long signal fast correlative algorithm,is presented.And it has been proved by MATLAB simulation and exact experiments:this scheme can solve part(<40%) overlapping of two waveforms,then,when the spectral width,measuring scope and grating spectral width are fixed,the number of multiplexed gratings increases greatly,and the precision reaches 1 pm.