Abstract: Based on the Shenzhen International Airport-Dayawan Intercity Railway Tunnel project, this study inves? tigates the improvement of synchronous grouting materials by using rock powder as a substitute for sand aggregate.The research focuses on optimization of rock powder substitution ratio, analysis of its influence mechanism, and permeability study of pea gravel, aiming to determine the optimal mix proportion of new grouting materials and compare their performance with traditional materials. Key findings include: (1) When the substitution ratio of rock powder increases from 0% to 30%, the fluidity of grout gradually improves with extended setting time, as smooth-surfaced fine rock powder replaces silty-fine sand; (2) From 30% to 70% substitution, cement hydration degree decreases,causing reduced fluidity and prolonged setting time. So the optimal substitution rate of rock powder is 30% with 17.8% increase in fluidity compared to original material ; (3) The orthogonal test-derived optimal mix ratio (cement∶fly ash∶bentonite∶fine sand∶rock powder∶water = 224.9∶432.6∶30∶548.3∶281.6∶500) demonstrates superior fluidity and setting time while meeting specifications, effectively preventing pea gravel grouting voids in field applications.