Most of the present studies on bridge damage identification using curvature modes only take one-dimensional single-beam structure as the research object. In this paper the idea of G-M method is put forward and the wide multi-beam structure is transformed into orthotropic plate based on thin plate vibration theory. The curvature expressions of the two orthotropic directions of the structure are obtained by analogy beam bending theory. In consideration of the deficiencies of the damage identification of the bridge by using single-order curvature mode difference index, two-direction multi-order curvature mode change rate superposition index for damage identification is used instead, and finally the finite element software Ansys is adopted to establish a bridge model to calculate the unit location, multi-location and different degree of damage under various working conditions. Matlab plotting results show that the index along the bridge longitudinal superposition is more accurate with less disturbance to the data of undamaged location and more index independence, and it can be used to locate the damage of wide multi-beam structure.