Abstract: In view of the problem of fractures expansion in coal and rock interface in coal seam containing gangue, based on the theory and method of linear elastic fracture mechanics, the expansion path and discriminant criterion of hydraulic fracture height of coal seam containing gangue at the interface between coal seam and dirt band are analyzed. The relationship between the expansion distance of the interface with high penetration and the water pressure inside the seam is discussed. There are three modes of seam height expansion in the coal-rock interface, including stopping extension in coal seams, extending along the interface and penetrating into interlayer. When the crack passes through the interface between coal seam and gangue and enters the dirt band, the stress intensity factor is calculated with the superposition method, and the calculation method of the expansion distance in gangue after the crack height passing through the interface is obtained. It can be seen from the engineering practice that the expansion distance of the penetration interface of the fracture height increases sharply with the increase of water pressure in the hydraulic fracture.