The invention discloses a building structure seismic damage assessment system and a method based on a wireless sensor network. The system mainly comprises a plurality of wireless sensor nodes and a control computer center which are wirelessly connected. With the help of the characteristics of low cost and self-organization of the wireless sensor network technique, the building structure seismic damage assessment system based on the wireless sensor network is constructed, and the goals of zero line arrangement and long-term all-weather working are really realized from the aspect of functions. By using detected acceleration and angular velocity responses for conducting numerical analysis and calculation to obtain the velocity response and the inter-story displacement response of a structure, seismic damage assessment cannot only be conducted to the overall structure and structural members through inter-story displacement, but also can be conducted to nonstructural members such as velocity-sensitive or acceleration-sensitive members through the velocity and acceleration responses of the structure, and the performance-based seismic damage assessment requirement of the building structure is really met.