Abstract: The fill sediments deposited on the lake margin slope during the Oligocene-Miocene, front Aerjin shan, western Chaidamu basin, were composed of the alluvial-lacustrine and fandelta-lacustrine sedimentary systems.The deposition of the two kinds of sedimentary system were controlled by the lake-level changes episodically. There are two types of sedimentary sequences. The sequence at high lake-level stand consist of fandelta- lacustrine system in which there are some important deposition microfacies such as fandeita plain ( lakeshore channel, subwater distributary channel and interchannel) , front fandelta (overflow deposits and front sheet sediments) and fandelta-front.The sequence at low lakelevel stand come from alluvial fanlacustrine system.Under the condition of basically balance between basin subsidience and sediments accumulation rate, replacement of the sedimantary systems was dependent on the lake條evel fluctuationes. Sedimentary processes of the fan delta and its fades distributary influenced by lake-level changes is different from ones of the fault depression basin margins. Relationship between alluvial fan and lacustrine at low lake-level stand is also distinguish from the normal facies model in addition to gravity flow deposits that originate from flood water channel.