Abstract: In Chinese seismic codes three types of normalized design response spectra with great difference are specified. The classification of normalized spectrum only depends on the site condition. The influences of other factors are neglected. Nevertheless the Classification standard for determining the category of a site is so rough that the difficulty will be liable to arise in classification of practical construction site. In view of this situation a new method of classification in which the overburden thickness are regarded as a main index is proposed. However the category of this site classification sometimes should be modified depending on the rigidity and composition of site deposits.A rough method of site classification depending on. the average S-wave velocity within shallow depth of site foundation is suggested when the detailed geological data are unavailable. Finally a set of site dependent average spectra are presented.