【Objective】 To generate a representative time history set of entirely non-stationary seismic motion processes that adhere to the design response spectrum stipulated in the codes for seismic design of highway and urban bridges.【Method】 An evolutionary power spectrum model for entirely non-stationary seismic motion pro cesses was initially formulated by integrating the intensity-frequency modulation function,pertinent to non-sta tionary seismic motion processes,with the Clough-Penzien power spectrum model,applicable to stationary seis mic motion processes. The parameters for this evolutionary power spectrum model were subsequently calibrated in accordance with relevant specifications. According to the spectral representation approach for the simulation of entirely non-stationary seismic motion processes,a MATLAB program was written to generate a representative time history set of the entirely non-stationary seismic motion processes. The fitting error between their mean re sponse spectrum and the code response spectrum was calculated and iteratively corrected. 【Result】 The parame ters of the evolutionary power spectral model for different site classifications and design earthquake groups were derived based on the codes for seismic design of highway and urban bridges. The generated representative seis mic time history set exhibits the typical characteristics of entirely non-stationary seismic motion processes,dem onstrating a satisfactory overall fit between its mean response spectrum and the code response spectrum,with an average relative error within 5%. 【Conclusion】 By employing the evolutionary power spectrum model,a MAT LAB program can be devised to simulate the spectral representation method of entirely non-stationary seismic motion processes. It successfully generated a representative time history set that complied with the requirements of the codes for seismic design of highway and urban bridges. The mean response spectrum of the generated time histories is consistent with the code response spectrum,verifying the effectiveness of the given method and MAT LAB program. This provides reliable seismic inputs essential for the seismic performance evaluation of bridge structures.