Selection of ground motion records forms the basis for incremental dynamic analysis ( IDA ) . In order to study the influence of spectral characteristics and duration of ground motions on the results from IDA, four conventional methods to calculate the characteristic period of ground motions are introduced, by which the record groups of ground motion are selected, compared with the response spectrum . IDA is carried out in accordance with the selected inputs of ground motions, then the IDA curves and fragility curves are discussed. On this basis, the influnece of earthquake duration on IDA is analysed according to two duration principles. It is shown from the results that the Spectral characteristics of ground motions influences evidently not only the values but also the degree of dispersion of IDA, and sufficient duration time is good for the stability results of IDA.