Abstract: In order to satisfy the requirements of seismic analysis for the structure,system and components（SSCs） in Nuclear Power Plants（NPPs）,two typical methods（modify the Fourier amplitude spectra in frequency domain and superimposing wavelet in time domain） were used to generate the artificial time history matching the Floor Response Spectra in NPPs.Numerical examples demonstrate that the time domain method is better that the frequency domain method in the matching precisions to the target spectra（especially the multi-damping spectra）,preserving the nonstationary character and baseline drift correction.However,the frequency domain method can maintain the phasing of Fourier components of the initial seed time history,which meets the requirements of the nonlinear structural analysis problems in SRP 3.7.1.