An inverse method is introduced to estimate the strain distribution by using the reflection spectra characteristics measured from the grating sensor. The improved transfer matrix method is used to simulate the spectral response of various strain distribution functions， and the variations between the spectrum shapes and the strain distributions are analyzed. The finite element method is used to calculate the strain fields of the specimens subjected to static bending loads， then the spectrum of the sensor is reconstructed. Furthermore， the correlation between the strain distribution and the form of the spectrum is verified by comparing it with that obtained by numerical simulation with the strain distribution function. In addition， a flexure test system for aluminum alloy plates with different radii holes is constructed to test the relationship among bending deflection， hole radius and the reflection spectrum characteristics. From theoretical calculation and experimental results， the measured spectra are found to reproduce the change in the simulation results very well， and the spectral feature parameters are proposed as effective indicators for the quantitative evaluation of the hole size， which has a potential to be applied to other configurations.