The invention provides a detachable cantilever bracket and a construction method of steel-concrete composite bridge concrete flange using thereof. The cantilever bracket comprises a steel bracket, a bolt, a nut, a round steel rod, a steel backing plate and a rotation limiting device; the obtuse angle end of the steel bracket is provided with a connecting plate, and the acute angle end of the steelbracket is provided with a steel sleeve; the nut is arranged above the through hole of the protruding part of the flange on the steel beam; one end of the round steel rod is fixedly connected with the steel backing plate, and the other end of the round steel rod penetrates through the steel sleeve; the steel backing plate is in contact with the steel beam web plate; internal threads correspondingto the external threads on the round steel rod are arranged in the first limiter and the second limiter of the rotary device. The first limiter and the second limiter are sleeving on the round steelrod through external threads and internal threads and are respectively positioned at two ends of the steel sleeve, and the steel sleeve is fixed on the round steel rod. The cantilever bracket and theconstruction method of steel-concrete composite bridge concrete flange using thereof can realize the rapid installation and disassembly of the cantilever bracket, improve the construction speed, savethe use cost and have no damage to the structure.