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 round steel rod, a steel backing plate and a rotation limiting device; the shape of the steel bracket is an obtuse angle triangle, and the obtuse angle end of the steel bracket is provided witha connecting plate; the acute angle end is provided with a steel sleeve; 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; the rotary limiting device comprises a first limiter and a second limiter; internal threads corresponding to the external threads on the round steel rod are arranged in the first limiter and the second limiter. The first limiter and the second limiter are sleeving on the round steel rod 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 the constructionmethod of steel-concrete composite bridge concrete flange using thereof can realize the rapid installation and disassembly of the cantilever bracket, improve the construction speed, save the use costand have no damage to the structure.