During the research of hydraulic structure model test，the displacement and strain of dam body and dam foundation are mainly measured by displacement transducers and foil resistance strain gauges on the surface．For the internal deformation of model under overloading，it will be difficult measured accurately with conventional monitoring instrument．In the research，based on gravity dam section，fiber grating sensors were installed in dam body and dam foundation，the internal displacement of structure model after overloading was monitored，as well as displacement transducers and foil resistance strain gauges on the surface. Through the comparison analyses of monitoring result of deformation for dam body and dam foundation measured by the fiber grating sensor and displacement transducers，the displacements measured using the fiber grating sensor are in good agreement with those from displacement transducers. The feasibility of the application of fiber grating sensor in gravity dam structure model test was confirmed．The test results reveal the overloading coefficient is 6.0，and the failure mechanism of the gravity dam structure model was obtained．The success application of optical fiber grating sensor in hydraulic structure model test will help sufficiently us to find out the internal deformation of dam body and dam foundation under overloading．
