Abstract: It is difficult to characterize and determine the high heterogeneity of the internal structure and the strong variability of permeability in the fracture core and fracture fracture zone in the fault tectonic zone. The relationship between the permeability and internal structural characteristics of different structural units in Beishan fault zone was studied by observing the microscopic structure, grain size characteristics, pore characteristics, in-situ water pressure test and laboratory penetration test. The research results show that: It is concluded that fault gouge is developed in the fault core, and the structural plane of structural dislocation can be seen in the fault core of Shiyuejing. The laboratory permeability test shows that the permeability coefficient of fault gouge is about 2×10^-11~5×10^-11m·s^-1. No anisotropy of the vertical and lateral permeability characteristics of fault gouge is found. The structure and geological origin of the Shiyuejing fault fracture zone and F₄ fault zone are described with the method of three-dimensional fine trough. According to the borehole water pressure test, the permeability coefficient range of the core fracture zone of Shiyuejing is 1.32×10^-5 m·s^-1 to 1.94×10^-5 m·s^-1, and the permeability coefficient in the core of the F₄ fault is generally greater than 2.4×10^-6 m·s^-1. Laboratory permeability tests of the samples in the Shiyuejing fault zone show that the permeability coefficient of the fracture damage zone is generally between 10^-9~10^-6 m·s^-1, and its P-Q curves show typical laminar flow type, filling type and erosion property. The permeability capacity of the sample increases with the increase of the number of fractures contained in the zone.