Combining with the advantages of evolutionary spectra theory and orthogonal HHT method, a method for the simulation of ground motions was established, which could simulate both non-stationary strength and frequency. Two harmonic-like long-period seismic records from Chi-chi Earthquake in Taiwan 1999 were selected as the original sample to simulate the long-period ground motions. The orthogonal HHT method was adopted to study the local spectral density and energy distribution of the artificial harmonic-like long-period ground motion samples. It was shown that the artificial ground motion samples obtained in the proposed method had an agreement in energy-time-frequency distribution with the original ground motions. It also has a good performance in the compatibility of elastic and elastic-plastic response spectra. The artificial harmonic-like long-period ground motions obtained in the proposed method can be used in the seismic response analysis of engineering structures.