A wireless sensor network system for automatic diagnosis of damage level of structures under strong seismic loading is presented in this paper. Restoring force characteristics and dissipated energy of the structures under strong seismic loading can be computed on sensor node using measured acceleration data. The acceleration data are measured by accelerometers installed on the top and the bottom of the structures. Wireless sensor network is used to compute and collect the data. Using this system, the information of restoring force characteristic and dissipated energy can be created on-board.