The invention relates to a nano gold-silver alloy solution having affinity for fibers and a preparing method thereof. The preparing method comprises the steps that silver ions and gold ions are addedinto a deionized aqueous solution of amino end group hyperbranched polymer, stirring heating is carried out, a nano silver solution and a nano gold solution are made, and are mixed according to the proportion, a high-temperature hydrothermal reaction is carried out, cooling is carried out, and the nano gold-silver alloy solution of a core-shell structure is made; the nano gold-silver alloy is torispherical, and the grain size ranges from 2 to 30 nm; the nano gold-silver alloy solution can be completely absorbed on the fiber surface at the high temperature, in the use process, silver ions are not released, good biosecurity is achieved, the solution has the strong molecular recognition and combining capacity for fibers such as cotton, silk, wool, calcium alginate fiber, and chitin, through normal temperature or high-temperature water bath, the solution can be completely assembled on the fiber surface, and the problems that the nano material and the fibers are poor in affinity, load efficiency is low, and environment is polluted are solved.