When the fiber Bragg grating is multiplexing， the limited source bandwidth may cause spectral overlap， then affects the accuracy of demodulation. A new type of fiber Bragg grating overlapping spectrum demodulation method is proposed. This method is based on an improved manta ray foraging optimization algorithm.The Tent chaotic map is used to optimize the initial population， and the differential evolution algorithm is used to optimize the individual location update strategy， which solves the problem that the manta ray foraging optimization algorithm is easy to fall into the local optimum. The simulation and experimental results of multiple fiber Bragg gratings overlapping spectrum show that the proposed method can accurately demodulate the center wavelength of the overlapping spectrum， even in the case of spectral distortion， the maximum error does not exceed 0.01 nm； at the same time， it effectively reduces the probability of fall into local optimum，and improves the stability and reliability of the algorithm.