The reinforced impervious soil-nailing wall is a new type of supporting system composed of soil nail and impervious wall, which has high water impermeability with high strength but low cost, and is suitable to foundation pit supporting engineering in silt and sand formation. Analysis was made on supporting mechanism and stress characteristics of the reinforced impervious soil-nailing wall in combination with a case of foundation pit engineering in Guangzhou, and conclusion was drawn that the characteristics of reinforced impervious soil-nailing wall, which was similar to ‘gravity retaining wall’ in range of bolt, came from the interaction of pressed grouting bolt, mixing piles and steel pipe pile. The monitoring data show that this foundation supporting system has sufficient safety reservation, and can be extended to foundation pit supporting project in similar formation.