<p>Earth pressure monitoring is essential for evaluating soil mechanical behavior and assessing geotechnical stability. Conventional resistance-based earth pressure sensors, typically encapsulated in rigid housings, often overestimate in-situ stresses due to stress concentration effects at the soil–sensor interface. This study presents a flexible earth pressure sensor based on Fiber Bragg Grating (FBG) technology, which integrates the high-resolution wavelength sensing capability of FBGs with the mechanical compliance of an elastomeric matrix. The sensor’s performance was evaluated through physical model tests conducted across multiple soil gradations and loading protocols, and directly compared with that of a conventional rigid resistance-type sensor. Experimental results indicate that the flexible FBG sensor achieves a substantial reduction in measurement deviation (R² = 0.98) relative to Boussinesq analytical predictions. Under cyclic loading within the elastic range, the flexible sensor exhibits near-ideal hysteresis behavior, returning to its initial state with a hysteresis loop area less than 5% of the loading curve area. In contrast, the rigid sensor displays noticeable residual deformation under identical conditions. These findings demonstrate that the flexible FBG sensor effectively mitigates stress concentration artifacts and provides improved accuracy for both static and dynamic earth pressure measurements in granular media.</p>