To analyze the transverse seismic performance of a large—scale beam aqueduct by considering the water mass influence，the aqueduct of the South to North Water Diversion Project is studied．Through a study of the fluid—structure coupling dynamical action method，we use an equivalent of a spring—mass system(simplified using the Housner water model)for simulating the dynamic interaction of the fluid and the aqueduct structure．The ANSYS finite element software is adopted to estimate the performance of a large-scale aqueduct with a beam．With the time history analysis method，we have investigated the transverse seismic response of the large-scale beam aqueduct using a few types of earthquake waves．Then，the natural vibration characteristics and the seismic response of the large-scale beam aqueduct are obtained considering the fluid-structure coupling interaction．The calculation results show that the water shaking function has a considerable influence on the dynamic characteristics of the aqueduct．The transverse seismic response of the beam aqueduct is significantly influenced by the water mass in the aqueduct．The water shaking function can effectively decrease the seismic response of the water itself．The transverse seismic response of the aqueduct is underestimated if the water in the aqueduct is ignored；however，if all the water in the aqueduct is regarded as a rigid body and appended to the aqueduct，the seismic inertia action of the water is seriously exaggerated and is unreasonable．Consequently，in the dynamic analysis of the large-scale aqueduct-we must consider the fluid-structure coupling interaction．We compare a case in which the fluid-structure coupling interaction is considered and that in which the fluid-structure coupling interaction is not considered；the former's maximum top displacement and bottom moment and the shear of piers are far less than those of the latter．Therefore，we conclude that the water mass influence on the seismic response of the aqueduct is limited．We compare the seismic responses of two different conditions of full trough(considering the fluid—structure interaction)and empty trough and find that the former7S maximum top displacement and bottom moment and the shear of piers are all greater than those of the latter．This is because the thankful water increases the quality of the upper portion of the aqueduct structure，which increases the seismic forces acting on the aqueduct．In the aseismic analysis of a large aqueduct，the influence of the water mass should be taken into account．When the water mass remains unchanged，and the aqueduct body changes according to the depth—width ratio，the natural frequency of the water in the aqueduct and the natural frequency of the aqueduct vibration change；however，the changes are not considerable．The change of the largest displacement of the piers on the top and the greatest moment and shear of the piers at the bottom depended on the depth—width ratio．Therefore，while selecting an aqueduct section，we should take the depth—width ratio of the seismic response of the piers into account．To some extent，the selection of a reasonable section can reduce the seismic response of the aqueduct．The fluid—structure interaction of the fluid and the aqueduct should be known for the estimation of both the impulse pressure and the convection pressure．The sloshing fluid produces a complex reaction on the aqueduct body；hence。we cannot simply consider all water quality values to be the added mass to the aqueduct body．