A dechlorinating agent for blast furnace top gas prepared by the steps of: selecting industrial limestone, commercial sodium carbonate and potassium hydroxide; soaking the raw industrial limestone in a potassium hydroxide solution, wherein a concentration of the potassium hydroxide solution is 10%-15%; heating the soaked limestone at 700° C. for calcination; grinding the light-burned limestone obtained by calcining the limestone and sodium carbonate until the particle size is below 20 μm; mixing the light-burned limestone and the sodium carbonate at a proportion of 30-70:70-30 for 10-15 min; grinding the resultant mixture by milling process until the particle sizes of all powders are less than 80 μm; adding 3% bentonite in the prepared mixing powder and fully mix the mixture; pelletizing the mixture with atomized water using a disc pelletizer; and selecting pellets of 3-10 mm in size; drying the said pellet at a temperature below 100° C.