The invention relates to a scale removing reagent and a using method thereof. The scale removing reagent comprises the following components in percentage by weight: 2.0 to 6.5 percent of citric acid, 3.0 to 13.0 percent of sodium bicarbonate, 12.0 to 18.0 percent of sulfamic acid, 1.2 to 2.5 percent of hexamethylene tetramine, and 60.0 to 81.8 percent of water. The using method for the scale removing reagent can be changed according to the capacity and scale thickness of a utensil to be subjected to scale removal; the scale removing effect is good, harmful substances cannot be generated, and the utensil subjected to the scale removal cannot be harmfully corroded; and the scale removing reagent is safe and practical.