Abstract: There are lots of proposed analytical models for strong ground motions, but it is difficult to choose a befitting one. Therefore, in the view point of practical engineering, the power random spectra of strong ground motions are summarized. Then the consideration of two basic conditions (the energy of strong ground motions is finite and the power random spectrum is zero when the frequency is zero, which are necessary to power random spectra of strong ground motions) is taken. Based the two basic conditions and the analytical result of 9 power random spectrums, an improved power spectrum of strong ground motions model is putted forward, and the rationality of the improved power spectrum is analyzed.