The present invention discloses a water-soluble granule formulation of 2,4-D salt, comprising components in the following weight percent: 5-80% 2,4-D salt (calculated as 2,4-D acid), and a water-soluble filler as the balance. The water-soluble granule formulation of 2,4-D salt has an outstanding control efficiency on annual or perennial Poaceae weeds and some broadleaf weeds in fields of soybean and other Fabaceae plants, for example, such weeds as amaranth, knotweed, lamb's-quarters night shade, siberian cocklebur, barnyard grass, foxtail grass, digitaria sanguinalis, broomcorn millet and the like. The formulation is environment-friendly, and has the advantages of being free of organic solvents and dusts and being easy to measure in comparison to conventional emulsifiable formulation, wettable powder formulation and suspension formulation. The present invention also discloses the preparation method of the formulation. The production process is simple, economical and safe. The whole production process, without the use of dangerous chemicals, is easy to control and operate and has a high safety factor.