This paper studies Chang 9 sandstone reservoirs of Triassic Yanchang Formation in the Longdong area. The results show that there are develop the distributary channel and underwater distributary channel sandbodies of shallow-water deltas. The sedimentary facies control the distribution of reservoir sandbodies, and the compaction, cementation and dissolution control the pore structure and physical property. The reservoir sandstones of Chang 9 oil-bearing layer can be classified into four types. The most advantageous microfacies are distributary channels, underwater distributary channels and mouth bars of the shallow-water delta.