Alluvial fans，which are important reservoirs for hydrocarbon accumulation，are characterized by complex internal structures and strong heterogeneity. Three alluvial fans（Quanjihe Fan，Shaliuhe Fan，Lanniwan Fan）developed in the north of Qinghai Lake were divided into several subfacies and several microfacies based on field surveys and analysis of remote sensing images. For Quanjihe Fan and Shaliuhe Fan，braided channel，main channel and interchannels were identified at the fan roots；braided channel，channel bars，sheet flood and noncohesive debris flow were identified at the fan middle；sheetflood and mudflat were identified at the fan margin. Two periods of debris flow and one short period of traction flow happened during the development of Lanniwan Fan. According to the sedimentary characteristics，the evolution processes of Shaliuhe Fan and Quanjihe Fan can be divided into 4 stages：the initial debris flow deposition and the development of main channel，noncohesive debris flow deposition，extensive development of braided channel and migration of channels and development of the delta. And the evolution processes of Lanniwan Fan can be divided into 3 stages：the early debris flow deposition，the intermittent traction flow deposition and the late debris flow deposits. The results show that the differences in provenance are the main causes for the differences in sedimentary characteristics for the 3 modern alluvial fans.And climatic factors，including humidity and wind field，control fan deposition too.