In process of drilling deep well DS-1 and DS-001 on Daxingchang Tectonic in Sichuan Basin, because of serious sloughing in Emei basalt layer, causing sticking accident, the well was forced to make 3 times toStamp the hole well and then to sidetrack,complex drilling accidents seriously hinder exploratory development of deep gas resource. Using microscopic observation, cast thin section, X— ray diffraction, cuttings roller recovery experiment, and mechanical testing means of rock testing study on Emei basalt, the results of the experiments show that, Emei Basalt does not contain clay minerals, natural fracture and weak bedding in rock mass are an important cause of wellbore instability. During the normal drilling, drilling fluid filtrate into the formation along the internal micro cracks, the pore pressure increases, the friction force between the drop and joint seam filling dissolution induced intensity is reduced, resulting in wellbore instability.