Abstract：In consideration of the difficulty of monitoring internal deformation in dam model tests，a new optical fiber sensor based on fiber Bragg grating(FBG) technology has been developed. Quasi-distributed FBGs are installed on a slender bar(circular cross-section) along axial direction to make an FBG sensing bar. For the dam physical model in this study，FBG sensing bars can be embedded in predrilled holes within the dam structure and the dam foundation. When the dam is loaded by hydraulic jacks and dam deformations occur，the sensing bar works like an elastic beam under arbitrary transverse and axial loading. According to the bending beam theory，the distribution of both horizontal and vertical displacements can be calculated from the strains measured by the FBGs. The two sensing bars used in the test were calibrated in the laboratory before testing. The calibration results have shown that the displacements measured by the sensing bars were in good agreement with those obtained using other conventional gauges. Recently a two-dimensional gravity dam model was constructed and instrumented with two embedded FBG sensing bars，together with surface mounted displacement transducers and strain rosettes. In the overload test，all the sensors were used to perform real-time monitoring of the model dam deformation. Major monitoring results are presented，compared and analyzed. The displacements measured by the FBG sensing bars in the dam model test are in good agreement with those from displacement transducers. The test results also reveal the deformation mechanism and failure mode of the gravity dam
