In order to sufficiently exert the efficacy of reservoir formation improvement,the propagation and distribution of cracks generated under hydraulic fracture were simulated with the plastic damage finite element method. In addition,the interva design for the multistage fracture of horizontal well in the tight sand reservoir of certain oil field with length of 400 m was optimized and selected. The volume density of micro cracks in the reservoir formation caused by injection fracture was mathematically express...