Abstract: To improve water flooding effects and enhance the oil recovery of ultra-low permeability reservoirs passessing a high water cut, reservoir geomechanics, engineering and numerical simulation were combined to reveal the opening mechanism and propagation of dynamic fractures and define the pressure limits required to open fractures in different directions. When injection pressure exceeds minimum horizontal stress, dynamic fractures will open in the orientation of maximum horizontal stress.High injection pressure and low stress difference between maximum and minimum horizontal stresses would result in a low-angle between injection-production well orientation and the maximum horizontal stress direction, in which multiple dynamic fractures might be generated in various directions.Effective infilling modes and optimized spacing for reservoirs with different well pattern could help to improve water flooding effect and dramati-cally enhance the recovery of hydrocarbon, along with avoiding frac interference.The proposed development mode as linear water flooding well pattern along maximum horizontal stress, lateral matrix displacement, limit injection pressure and control multiple fractures opening, provides a new approach for improving water flooding recovery in ultra-low permeability reservoirs.