In order to explore the stress evolution and roof deformation and failure law of horizontal sublevel mining face in steeply inclined extra-thick coal seam, this paper takes Baiyanzi Coal Mine in Gansu Province as the engineering background, analyzes the evolution law of stress field and displacement field of coal and rock in different sublevel mining processes through numerical calculation, and reveals the deformation and fracture characteristics of roof rock beam combined with theoretical analysis. The results show that the stress of surrounding rock in multi-section stope of steeply inclined thick coal seam presents asymmetric distribution characteristics. With the increase of mining sections, the stress concentration of coal and rock on both sides of roof and floor occurs. Under the combined action of roof extrusion and goaf pressure relief, the stress concentration degree of coal rock on the roof side is further enhanced, and the stress peak area is close to the deep part of the working face on the roof side of the lower part of the goaf. The peak value of the concentrated stress increases linearly and positively, and the stress concentration coefficient reaches 2.53. The deformation mode of coal and rock changes from the settlement of coal above to the migration of roof strata to goaf, and the fracture range of overlying strata gradually extends above the roof. The roof rock beam is constrained by the non-uniform filling of broken rock blocks, and the peak deflection is located in the middle and upper regions, which is prone to tensile deformation and failure, causing surrounding rock disasters. Roof pre-splitting blasting can slow down the degree of mine pressure appearance.