Abstract: Abstract: [Objective] Aiming at the problem of narrow dynamic range of optical fiber displacement sensor at present, a balloon long-period fiber grating (LPFG) displacement sensor with simple structure and easy preparation is designed. [Methods] Based on the simulation and optimization by RSOFT software, The measurement range is determined by the spectral shape of the optical fiber under different curvature. Multimode fiber balloon-shaped LPFG (MMF-BLPFG) formed by periodically embedding multimode fiber into single-mode fiber provides a reference peak for measuring displacement. Using the precise continuous cutting device as the experimental basis, the test samples consistent with the simulation results were prepared for testing. [Results] The maximum displacement measurement range of 36 mm was achieved by measuring the drift of two resonance peaks. [Conclusion] It has good application potential in large-scale measurement scenarios such as stability measurement and continuous monitoring of underwater drainage space piping system of ships.