Abstract: To identify the dynamic deflection of continuous beam structures based on their measured strains, a new technique to estimate the dynamic deflection of beam structures based on strain modes is proposed. The strain mode shapes are first estimated from the cross-correlation function of measured dynamic strain data. Then, the displacement mode shapes can be estimated from the strain mode shapes based on a displacement-strain relation. With knowing the strain mode shapes and strain data, the corresponding modal coordinates can be estimated. The dynamic deflection can then be estimated by the obtained displacement mode shapes and modal coordinates. The method is verified by numerical simulations of a simply support beam subjected to an impulsive excitation and an earthquake excitation. The experimental tests of a simply supported beam under various hammering excitations are also conducted to verify the effectiveness of the proposed method. Both the numerical and test results show that the proposed method can estimate the dynamic displacement of beam structures with a high accuracy.