Building foundation pit angle brace device

The utility model discloses a building foundation pit angle brace device which comprises an upper supporting frame and a lower supporting frame, the upper supporting frame and the lower supporting frame are both installed at the vertical wall corner of an underground diaphragm wall, the lower supporting frame is installed below the upper supporting frame, the upper supporting frame comprises two first triangular steel corbels which are arranged in an up-down stacked mode, and the two first triangular steel corbels are arranged in a staggered mode. The first triangular steel corbel comprises two first side steel plates which are perpendicular to each other, a first inclined plate and a second inclined plate, the first side steel plates are fixedly connected with the wall surface of the diaphragm wall through first expansion bolts, and the two ends of the first inclined plate and the two ends of the second inclined plate are connected with the first side steel plates; the lower supporting frame comprises a plur