Because loess grains are fine, it is difficult to study active faults in loess usingconventional methods. In order to obtain the related data of the faults, the authorstudied the loess samples from the Lintong-Chang'an fault, Northern Lishan slopefault and Chanhe fault east of Xi'an and analysed their microstructure types byusing SEM. On the basis of the contact relationships of coarse grains attd cementtypes, six types of SEM structures perpendicular to fault planes have been distin-guished, of which three are oriented structures and three are non-orientedones. Four SEM types of structures of sliding planes have been recognized, of whichtwo types are binding ones. Morphological types of neogenic minerals may fall incoseven types, of which two are oriented. Through analysis, the author believes thatthe sliding features (stick-slip or stable sliding) can be reflected by the associa-tion characters of these microstructure types in the same sample. The indicatorsof microstructures for stick-slip are oriented schistosity, random neogenic mineralsand non-binding sliding planes. In this paper, the E-W-trending faults in severalactive faults are mainly of stick-slip nature, while others show the features ofstable sliding. The former are closely related to earthquakes, while the latter haveno direct relation to earthquakes. To make such distinction is important to theevaluation of the regional crustal stability.