Abstract: The Baboshan fault zone consists of the inner branch fault,the outer branch fault and the Huangzhuang-Gaoliying fault,lying in the southwestern suburb in Beijing.Based on geological information obtained in the field and laboratory result,it is believed an overthrust of the Yenshan stage which has shown no activity at present;the outer branch,a normal fault which is small in its scale and offset;the only Huangzhuang-Goliying fault,an active fault which goes through middle Pleistocene loess.In order to gain further information in this regard,we have examined the surface features of quartz grains for 6 samples of gouge and 4 samples of relative formations obtained from the fault,using a new method to estimate activities of the fault,for which the scanning electron microscope has been used.The results coincide with the macroscopic information from the field.