Abstract: To improve the underwater acoustic detecting capability of DFB fiber laser, the optimization design and mechanism analysis of a sandwich-type encapsulated structure were carried out using FEA software ANSYS, by setting the relative acceleration sensitivity as objective function, the structural dimension parameters as design variables, and the structural first-order inherent frequency and sound pressure sensitivity of the probe as state variables. The analysis results show that when a 100 m unbalanced interferometer is used, the sound pressure sensitivity of the designed probe can achieves about -135.1 dB, and the relative acceleration sensitivity -19.6 dB. It is shown that by properly setting the thicknesses of the beams and arranging the connection joints, the DFB fiber laser hydrophone with the optimized encapsulated structure has high sound pressure sensitivity and improved anti-acceleration performance.