The invention discloses a novel deep building foundation pit supporting system which comprises front-line piles, a water-retaining curtain, a top beam, rear-line piles, an anchor rope and sand pulp, the front-line piles are positioned at the side of a building foundation pit, the water-retaining curtain is tightly abutted against the inner sides of the front-line pile, the rear-line piles are positioned in soil body at the inner side of the water-retaining curtain, the tops of the front-line piles and the rear-line piles are provided with the top beam integrally poured by reinforced concrete, wherein the top beam is provided with a protruding part towards the inner side at the top of the rear-line piles and is provided with the vertical anchor rope in the soil body at the inner side of the rear-line piles, the lower end of the anchor rope vertically extends into rock body and the sand pulp is poured into the rock body for concretion, and the upper end of the anchor rope is tightened with and is concreted with the protruding part of the top beam. Because the vertical anchor rope is arranged in the soil body at the inner side of the rear-line piles and the drilling in the soil body is fast and good, the invention greatly improves the speed, increases the construction efficiency, saves the time, reduces the loss of a drill bit, lowers the construction cost, and achieves better profit.