Based on the displacement of seismic design theory,this paper introduced the basic principle and implementation of capacity spectrum method.With the background of the south to north water diversion project,it studied the seismic performance of an aqueduct structure, and then compared with the results of nonlinear time-history analysis.Considering the particularity of aqueduct structure,when calculating the demand spectrum curve,it used constant ductility elastoplastic demand spectrum which based on the code for seismic design of hydraulic structures.Analysis show that capacity spectrum method can be used for seismic performance evaluation of isolated aqueduct.