The spectral parameters of a seismic random model have been studied on the basis of the design response spectrum in the Chinese standard Code for design of seismic of electrical Installations（GB50260-96）.First

the nonstationarity of the ground motion is represented with an envelope function

which defines the duration of the ground motion at same time.Then

the power spectral density（PSD） of the acce-leration at ground level is evaluated by an iterative approach according to the principle of equivalent peak acceleration.Finally

the Clough-Penzien acceleration spectrum is selected as a target function to calculate the PSD curve through nonlinear fitting on the parameters

such as earthquake intensity and site type

defined in the code.The results show that the Clough-Penzien spectrum can fit the PSD curve well.The spectrum parameters of the random model of ground motion are given in this paper

and they provide a re-ference for the selection of ground motion input.