Abstract: The bedding fault zone in the dam site of Baihetan Hydropower Station is characterized by large scale, strong penetrability and complex geological conditions, which can control the underground caverns.Due to the large scale, the effects of wavelength fluctuation of the bedding fault zone cannot be considered accurately by normal field tests, and the size effect analysis needs to be introduced. A systematic study on the mechanical parameters of the bedding fault zone is carried out. Combining with the mechanical strength parameters obtained by the field tests, and the size effects of the bedding fault zone are analyzed by introducing the digital close-range photogrammetry technology and the particle flow numerical method. The mapping laws of the mechanical parameters of the bedding fault zone with joint roughness coefficient, soft filling thickness and size effects are revealed. In the engineering application, taking the advantages of the research results of bedding fault zone, the dome shape of tailrace surge chamber of Baihetan Hydropower Station is optimized. The method can provide a reference for other projects.