There are two sets of conjugate shear fractures in the NE-SW and N-S orientations in Chang6 reservoir，Ansai oilfield. But the watered direction was inconsistent with the nature fractures. On the basis of analyzing the nature fractures characteristics，the produce curves，the injection index curves，the intake profiles and the time-lapse well test in different development stages of Wangyao area were used to study the response characteristics of dynamic fractures. Because of the increasing water injection pressure，the closed nature fractures opened selectively，expanded and connected oil and water wells，which caused the water flooding of oil zones. According to the Coulomb-Mohr shear failure theory and Griffith failure criteria，the opening pressures of dynamic fractures are 20-23 MPa and the ultimate extension directions are NE 60°-75° which is consistent with the current maximum horizontal major stress direction. The dynamic fractures aggravate the reservoir heterogeneity and cause the quick water flooding along the current maximum horizontal major stress direction，which reduces the producing degree horizontally and vertically and influences the reservoir development effects.