The invention relates to a method for preparing highly pure zinc sulfate heptahydrate from zinc-containing blast furnace gas sludge, and belongs to the technical field of comprehensive utilization of metallurgical resources. The method comprises the following steps: breaking, drying and grinding block zinc-containing blast furnace gas sludge, adding the ground zinc-containing blast furnace gas sludge to a sulfuric acid solution to carry out acid dipping, carrying out solid-liquid separation to obtain filter residues and a filtrate, adding a hydrogen peroxide solution and limestone to the filtrate in order to carry out oxidation, neutralization and iron precipitation, filtering the obtained filtrate to obtain iron-containing residues used for iron recovery and an iron removed solution; adding ZnF2 powder to the iron removed solution, stirring, reacting and precipitating the iron removed solution and the ZnF2 powder for 1-2 h, and filtering the obtained solution to obtain calcium and magnesium residues and a zinc sulfate solution; and sequentially carrying out evaporative concentration, cooling crystallization, dehydration and air drying on the zinc sulfate solution to obtain the highly pure zinc sulfate heptahydrate, and returning a mother liquor obtained in the dehydration process to the evaporative concentration process. The method effectively recovers the valuable element zinc from the blast furnace gas sludge, and allows the highly pure zinc sulfate heptahydrate to be prepared.