Abstract: Taking Longmaxi Formation of the Sichuan Basin as an example,the mechanism of interaction between hydraulic fractures and weak plane was investigated to further understand the hydraulic fracture propagation in layered shale.Such mechanism in fracturing was analyzed based on Mohr-Coulomb Criteria,and the critical pressure for rock matrix failure,weak plane shear and opening failure were also studied.According to fracture mechanics,the shear displacement under opening and shear failure of a weak plane were considered,and then an interaction theoretical model was developed and applied in shale reservoir.The calculation example showed that,the pressure in hydraulic fracture could stimulate the rock matrix-failure when 0° α 20°,the weak plane shear-failure when 25° α 75°,and the weak plane opening-failure when 80° α 90°;the shear displacement was jointly affected by frictional coefficient,shear stress(as the main factor)and normal stress.After the shear or opening failure of weak plane occurs,its displacement is proportional to fracture length and inversely proportional to elastic modulus.It was suggested that the theoretical model could be used in predicting the interaction between hydraulic fracture and weak plane,which was very consistent with the micro-seismic crack monitoring.