A method for forming a structural-strain sensor network on a structure is provided. The sensor network has plural nanocomposite sensing elements having high sensitivity, and can be quickly fabricated. The method comprises attaching a molding layer having openings onto the surface, and filling the openings with a coating material made of nanocomposite hybrid material. After immobilizing the coating material in the openings, the sensing elements are formed and the molding layer is removed. Electrical wires are formed on the surface such that two opposite electrodes are formed on each sensing element. The resistance between the two electrodes indicates a strain experienced. The sensor network finds applications in identifying a damaged location or an impact location on the structure for structural health monitoring. Voltage waveforms measured at the sensing elements are analyzed to estimate the damaged location or the impact location according to a guided-wave propagation model.