In this study, the method to estimate the bridge deflection is developed using the fiber optic Bragg-grating strain sensors. Most of the evaluation of structural integrity, it is very important to measure the geometric profile, which is the major factor standing for the global behavior of civil structures, especially bridges. In the past, for the lack of the appropriate method to measure the deflection curve of bridge on site, the measurement was restricted to just a few of discrete points along the span length, which were also limited to the locations installed with the displacement transducer in advance. Hereby, with an application of classical beam theory, a formula is established estimating the continuously deflected profile from the measurement of strains at several points. In addition, strains could be measured by the use of fiber optic strain sensors, which are electro-magnetic noisy-free, and into which several points of sensing could be installed. With the strain data acquired, the proper strain curve is fitted, and finally, deflection curve would be estimated. The experimental test was carried out to verify the developed algorithm.