Based on the detailed study of gravel fabric characteristics of conglomerate layers from the Lower Cretaceous Nanxin Formation in the Nanjian region, combined with the characteristics of the basin bedrock stratigraphy and lithologic characteristics of the surrounding tectonic belt, the gravel has complex composition, poor sorting, medium-good roundness and poor degree of weathering. This paper further discussed the property of the conglomerate layer, the material sources and the hydrodynamic conditions, climate, topography and tectonic setting. Our data shows that of Nanxin Formation were the coarse clastic products of alluvial fan and braided river facies in a semiarid to braided climate condition with rapid accumulation; The gravel pebbles suffered a strong physical and chemical weathering before deposition; The sediment source of the gravel was inferred to come mainly from the basal strata within the basin and the Ailaoshan tectonic belt to its eastern direction.