Abstract: The Longjiang bridge with a main span of 1 196 m is the first suspension bridge in high seismic intensity region in China. Frequent earthquake activities pose a serious threat to the safety of bridge structures. During the construction of the bridge, a health monitoring system was constructed, which included structure health monitoring points. Then a site strong motion observation system was deployed to optimize the seismic response observation of the bridge. This article mainly introduces the design scheme, system composition, communication methods of the site strong motion observation system. The observation results obtained from this system provide a basis judgment for the structural health of the Longjiang bridge under earthquakes action, and reliable ground motion input for the seismic response analysis of bridge structures. These results also deepen our knowledge of response characteristics under earthquake action and assist in seismic design research of long span bridges.