Abstract:  The modal analysis of the arch-braced U-shaped aqueduct structure is carried on by using three dimension finite element method in the conditions of the aqueducts without water‚with3．5m-depth water （adopted for the purpose of research）‚with designed-depth water and with ful- l depth water．The basic dynamic characteristics of aqueducts considering fluid structure interaction‚and the effects of liquid on the aqueduct structure are analysed‚which puts forward suggestions for the seismic design of aqueduct structures．

Key words:  U-shaped aqueduct, modal analysis, fluid structure interaction