Abstract: A π phase-shifted fiber Bragg grating theoretical model is established, and the effects of an asymmetric and symmetrical perturbation field on a phase-shifted fiber Bragg grating are investigated in this paper. The trends of wavelength shifting caused by effective refraction index of phase shift grating in symmetric and asymmetric acoustic field are investigated in detail. Then, the fiber laser acoustic sensors packaged in asymmetric and symmetrical structures are designed and tested, respectively. The results show that the acoustic response of the wavelength of the distributed feedback (DFB) fiber laser (FL) in an asymmetric packaging structure is much more sensitive than in that in the symmetrical structure. The sensor packaged in the asymmetrical structure has a better low frequency (0 Hz-500 Hz) performance and a higher sensitivity than that in the symmetrical structure, and the sensitivity is improved about 15 dB in average and 32.7 dB in maximum. It provides a new method to improve the sensitivity of the fiber acoustic sensor.