The invention discloses a method and device for determining the supporting strength of a large-dip-angle fully mechanized coal mining face, relates to the technical field of coal mining, and can solvethe problems that when a large-dip-angle coal seam is mined, the supporting strength of the large-dip-angle fully mechanized coal mining face cannot be accurately determined, and a working face support crush accident is easily caused. The method comprises: obtaining coal seam occurrence conditions and mining technical condition parameters of a target large-dip-angle working face; dividing the direct roof of the target large-inclination-angle working face into multiple sections of areas in the inclination direction according to the motion state of the roof, wherein the multiple sections of areas comprise a slippage section and an instability section; creating mechanical models of the sliding section and the instability section; and calculating the supporting strength of the target large-dip-angle working face based on the mechanical model and the coal seam occurrence condition and mining technical condition parameters. The method is suitable for determining the supporting strength of the large-dip-angle fully mechanized coal mining face.