An MS6.6 earthquake occurred on July 22,2013,in Minxian-Zhangxian,Gansu province,and the amplification effect of the loess site appeared in meizoseismical area.To explain the principle of amplification effect of loess site in theory,we measured and researched two typical loess sites by using microtremor measurement.The results show that,the damage of adobe house is more serious on the summit than on the gully.On the summit the damage of adobe house is serious and there are even entire collapses,but on thethe gully there are cracks and not collapse of adobe house.The intensity difference between the summit and gully is intensity Ⅰ~Ⅱ,which shows obvious amplification effect of the massif.In the paper,we have made contrastive study of the predominant frequency of microtremor measurement by choosing two typical areas of the obvious amplification effect of loess site at the meizoseismal area(intensity 8),which are Yongxing village and Daleng village,Majiagou village and Xinglin village in Meichuan town,Minxian County.At Yongxing village and Majiagou village,the damage of adobe house is serious and there are entire collapses.However,at Daleng village and Xinglin village,there are cracks and not collapse of the same adobe house.The earth pulsation has rich geophysics information,which is aggregation of body wave and surface wave.In the paper,the principle,test method and causes of ground microtremors are introduced.According to engineering examples,the determination for the predominant period of a site is described,moreover,its application in evaluation for the category of the site and soil and the effect of different site conditions on the characteristics of frequency spectrum are analyzed.The results show that the thick soil and thin soil structure obviously affect the frequency spectra of the ground microtremors,and there are corresponding relationships between them.The research results show:the characteristic of predominant frequency of the site is obvious in the covered loess area,in which the predominant frequency is lower on the summit than on the gully,the range of which is 1~2Hz and 3~6Hz respectively;Meanwhile,with the increase of the altitude of the loess site,which shows the distribution characteristic of thick loess,the range of the site predominant frequency is 1.3~1.8Hz,which is similar to the predominant frequency 1 Hz of earthquake observation wave and shows obvious amplification effect of the site,which is the same with the actual damage fact.