Palygorskite is a typical indicator mineral for arid and strong evaporation environment. The distribution of palygorskite in loess-red clay sequence may act as an important indicator for reconstruction of paleoenvironment and paleoclimate in ～7.0 Ma eolian sequence from the Chinese Loess Plateau.In this paper, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations on Renjiapo red clay-loess-paleosol profile in Lingtai, Gansu Province were performed. The results indicate that palygorskite extensively existed in red clay sequence deposits before 3.6 Ma, while no alygorskitehas been observed in the eolian sediments in the last 3.6 Ma, including 3.6～2.6 Ma red clay sequence and Quaternary loess-paleosol sediments. Micromorphology and microstructure shows that palygorskite is an autogenic mineral formed during pedogenesis. The results of this study indicate that the horizon where palygorskite disappeared in the red clay sequence was consistent with that of magnetic susceptibility enhancement, and eolian flux and dust depositional rate increased in about 3.6～3.2 Ma，which was a conversion period of east Asian monsoon type, during which paleomonsoon climate pattern shifted from summer monsoon dominated by sustainable dry_warm climate to east Asian paleomonsoon characterized by the alternation of winter monsoon with dry and cold climate and summer monsoon with warm and humid climate, noted for simultaneous strengthening of east Asian winter and summer monsoon.