Large span bridges have high towers and large spans with long natural-vibration cycle

and long vibration cycles ofground with thick and soft soil layers have significant effect on the bridge structures.The "Specifications of Earthquake Re-sistant Design for Highway Engineering of China（JTJ004-89）" can also be applied to girder bridges and arch bridges with amain span below 150 m

yet

there has been no anti-seismic design specification or guideline in China applicable to large spanbridges.In this paper

the author has performed seismic response analysis for ground with thick and soft soil layer in conjunc-tion with examples of large span bridge projects on the basis of the results of static and dynamic performance parameter in-situtests of ground soils and dynamic triaxial test

studied the seismological effect of ground with thick and soft soil layers

dis-cussed the design response spectrum characteristics of ground with thick and soft soil layer at different seismic intensities

andanalyzed the limit of current specification of design response spectrum in actual applications.The results have important guid-ing significance to relevant projects

and can also be used in the promulgation of aseismic design code for large-span bridges.