The invention relates to a soluble alloy used for manufacturing a fracture separating tool and a preparation method of the soluble alloy. The soluble alloy is classified as a soluble alloy material with low density, and is mainly used for a separating tool involved in an oil and gas field developing fracture construction process. The alloy is prepared by two steps of smelting of elements of Mg, Zn, Ca, Fe, Cu and Ni, and subsequent hot extrusion treatment. The alloy provided by the invention has the advantages of low density (about 1.8g/cm<3>), high mechanical strength, quick dissolution in an aqueous solution containing electrolyte, and the like, the alloy is used for manufacturing the fracture separating tool used in an oil and gas field fracture improving process, self dissolution and failure can be achieved after the use of the tool, procedures such as flowback, drilling and milling recovery and the like required by a traditional tool can be omitted, and the construction efficiency is improved.