The invention belongs to the technical field of resource recycling, and particularly relates to a technology for recycling nickel sulfate from nickel slag. The nickel slag is crushed into powder through a crusher; the powder is dissolved by adding a sulfuric acid solution, and filter liquor A is obtained through filtering after stirring; the obtained filter liquor A is cooled and crystallized, crude nickel sulfate crystals and mother liquor A are obtained, then pure water is used for dissolving the crude nickel sulfate crystals, and a solution B is obtained; hydrogen peroxide is added in the solution B or the solution B is inflated with oxygen, a sodium hydroxide solution is added for pH adjustment, sediments are removed through filtering, and a pure nickel sulfate solution is obtained; and the pure nickel sulfate solution is recrystallized, and nickel sulfate crystals and mother liquor B are obtained. The technology solves the problem of the reaction of excessive sulfuric acid and alkali, a large number of resources are saved, economic benefits are obvious, and environment pollution is effectively reduced.