On the basis of core description of11wells in the blockˉ6ofKeramay oilfield in the JunggarBasin，we recognize7types of lithofacies in the alluvial fan of the Lower Karamay Formation. In combination with sedimentary microfacies analysis，we study the quality differences and distribution of reservoirs within the alluvial fans by using core analysis and testing data. The pore space of the Lower Karamay Formation is dominated by primary intergranular pores. Depositional fabric controls the reservoir quality in the study area. The reservoirs of coarse sandstone facies and fine conglomerate facies are the best in the alluvial fans of the study area. The reservoirs of different microfacies are significant different in reservoir quality. The reservoirs of braided channel and gulley microfacies are the highest in quality，followed by the sandy gravel bars. The reservoirs of gravel bar and runoff channel microfacies are fair. The reservoirs of sheet flood microfacies are the worst. Gulley microfacies occur as narrow bands within gravel bars and sandy gravel bars，and act as the high trans mssibility pathways for reservoirs in the root fan and inner-middle fan.