The invention provides a method for preventing soft water from eroding equipment and pertains to the technical field of soft water. When soft water is adopted in recycling cooling water of the fire wall of blast furnace and air heating furnace, in order to prevent the soft water from eroding equipment, borate and copper slow-release agent are added in the soft water, the added amount of borate is 1200 mg/L to 2000 mg/L, and the added amount of copper slow-release is 1 mg/L to 2 mg/L. The advantages are that borate formulation is environmentally friendly with strong stability, and the shortcomings of phosphate formulation, nitrite formulation and silicate formulation are overcome.