A large number of coarse clastic rock deposits were developed in the Lower Cretaceous Xiguayuan Formation in the Luanping Basin. Using 3D digital model as well as manual photography of typical outcrops, combined with fluid transportation mechanism, microfacies identification, the debris deposits in fault depressed lacustrine basin were studied in detail. The results show that the northern part of Luanping Basin in the Xiguayuan Formation was affected by the boundary fault activity, and the nearshore subaqueous fan deposition system of the typical fault basin was developed. According to outcrop observation and research, three sub- facies including root fan, mid fan and fan end can be identified. Among them, the root fan sub- facies are characterized by the fact that the detrital clasts directly enters the lake, the lithology is coarse, the sorting is extremely poor with no rounding. The mid fan adopt the division method of “subaqueous channel micro- facies” and “marginal micro- facies”. The micro- facies of the subaqueous channel sediments were controlled by two different fluid properties of debris flow and turbidity flow that developed simultaneously. The boundary is clear and slightly scoured, the lateral continuity is relatively stable, the gravel has a certain orientation, the rounding is poor, and it is best developed in the mid fan.The marginal facies are relatively mixed, the boulders are more common, and the obvious plate is visible. Interlaced bedding, poor lateral continuity, indicating diversion or marginal deposition by rivers, and no development of erosion- filling structures. The fan end sub- facies are characterized by thin- interbedded sandstone or thick layer of fine sandstone, showing bioturbation structures and fine gravel layers. The microfacies division method has a causal basis. The research results provide a new idea for the identification of nearshore subaqueous fans in similar basins. The underground research and will be conducive to oil and gas exploration and development.