Since the mechanical properties of dam materials can directly affect the settlement deformation and structural stability of core wall DAMS, it is necessary to explore the mechanical properties of soil-rock mixture and the internal deformation and failure mechanism by means of macro and micro in order. Taking the Rumei Hydropower Station in Tibet in Lancang River as research background, particle flow code (PFC) method based on discrete element was used to carry out large-scale triaxial numerical simulation test. The results show that with irregular enhancement in the form of block stone, the stress peak nodes was in advance, peak strength increased obviously with significant softening characteristics, shear shrinkage was not obvious, and the dilatancy is prominent; The shear zone evolved from a single “工” shape to a complex “工” shape. The thickness increases from 45 mm to 105 mm, and the final swelling failure area increases exponentially to 35 000 mm². The extreme value and the number of force chain strength increased. Increasing the stone content was the key to improve the peak strength of the sample. When the rock content was low, the shear shrinkage characteristic was prominent, and the dilatancy characteristic was not obvious. With the increase of the stone content, the “gear” effect of the block stone was enhanced, and the shear zone failure mode was transitioned from smooth reverse “S” shape to multiple irregular shear zones, with the thickness increasing from 47.5 mm to 105 mm, the swelling failure area evolving from 12 800 to 35 000 mm², and the number of strong chains increased. The extreme strength of the force chain was increased from 10.49 kN to 164.30 kN. In conclusion, it is suggested to select blocks with high irregularity and increase the stone content to enhance the structural strength stability. The research can provide reference for the stability evaluation of the project in the later stage and the work of the proposed dam.