The Qaidam basin is located in the superposition area of PalAsia tectonic domain and Tethyan Himalayan tectonic domain. Complex tectonic stress results in the great relief in the basin. Southwest warm moist current hindered by Himalayan Mountains caused the climate arid. The alluvial fans were well developed under the special geological background. Four alluvial fans in the Da Qaidam area were investigated, including three subfacies and eight microfacies. According to the depositional environment and sediment characteristics, alluvial fan facies was subdivided into upper fan, middle fan and lower fan subfacies. The upper fan subfacies is composed of coarse sediments, and could be subdivided into channel, main canal and space between canal microfacies. The middle fan subfacies is composed mainly of fine grained sediments of high maturaty and could be subdivided into braided channel, space between channel and verticalbar microfacies. The lower fan subfacies is composed of the finest grained sediments among the three subfaces with the lowest fluid energy, and could be further subdivided into radial water channel and laminar flow microfaces. There is a great discrepancy of sediments among different kinds of subfacies. The channel, main canal and braided channel microfaces have good reservoir properties. It is proved by exploration that oil pools with selfprotection ability could be formed in the Internal of alluvial fan facies; Fan anticline Reservoir above the jacent stratum and base rock weathering crust Reservoir could be formed with alluvial fans formation.