Abstract: The microtremor characteristics of the construction site can reflect the geological information of the formation structure to a certain extent. In recent years, it has been applied in the engineering geological investigation, but the mechanism of the generation of microtremor and the relationship with the formation structure have yet to be further studied. This paper chooses the areas with the same strata structure which has large undulating in the layer's level, and then half-year microtremor tests had been done based on the study of the method of H/V spectral ratios. Then the researches on the change of cover thickness of the large undulating formation which had an effect on dynamic characteristics and time characteristics of the microtremor is done by H/V spectral ratio method to process and interpreter data. These results show that the H/V spectrum transformed from a single peak to two, and finally to the platform with the cover thickness decrease. The range and frequency of the peak is gradually increased, while the spectral ratio is decreased. The morphology of H/V spectrum appears a peak platform with high frequency values and large range, which is extremely unfavorable to the seismic resistance of low rise buildings with relatively high natural frequency, and it should be given enough attention in the study of seismic hazard assessment.