Abstract: Under the influence of stresses unloading after mining, the fracture and instability of the interbedding and combined structure system of deep rock mass is one of the main causes of water inrush in the longwall face. In order to study the influence of confining pressure unloading(CPU)on the fracture of rock mass combined structure in deep coal mining, the triaxial loading, unloading-seepage tests of primary coal-rock mass(PCRM)were carried out in the laboratory. The classification characteristics of PCRM under different initial confining pressures were obtained. And the strength characteristics of the starting point of axial compressive stress unloading and the terminal point of confining pressure unloading and the mechanical mechanism of the dominant fracture modes were studied. Combined with CT scanning and three dimensions reconstruction techniques, the unloading fracture geometric characteristics of PCRM were obtained. The relationships between the unloading level of confining pressure and the tensile fracture and shear fracture of rock mass were established. And the relationships between the fracture modes of CPU and the sharply increase of the permeability were revealed. Meanwhile, the dominant unloading fracturing modes of PCRM under different initial confining pressures were verified and determined. The results show that under the joint action of CPU and axial pressure loading, the dominant fracture modes of PCRM mainly include three types, and they are tensile fracture, shear fracture induced by CPU,and the fracture induced by the axial compressive stress unloading coordinated with CPU,respectively. With the increase of initial confining pressure, the critical value of unloading terminal point of confining pressure for the tensile fracture and the unloading starting point of the axial compressive stress for the shear fracture increase linearly. The CPU can cause the synergetic unloading of the axial compressive stress drop suddenly, that could drive primary crack structure in the coal-rock interface and bedding plane to annularly open or tensile fracture, and they mainly link with inclined and vertical cracks. Besides, both tensile fracture and shear fracture mode induced by CPU can cause the permeability of PCRM suddenly increase, the fracture mode at the sudden increase point of the permeability is closely related to their critical values of the unloading level of confining pressure.