The invention belongs to the technical field of resource recycling, and particularly relates to a method for recycling nickel sulfate from nickel slag. The method comprises the steps that nickel slag is smashed by a smashing machine to be powder; strong acid is added for dissolving and stirring, and a filtrate is obtained after filtration; hydrogen peroxide or oxygen is added into the filtrate, a sodium hydroxide solution is added for adjusting the pH value, and filtration is carried out; the filtrate is cooled and crystallized, and nickel sulfate crystals are obtained; and the obtained nickel sulfate crystals are roasted to obtain nickel sulfate powder. The decomposition temperature of nickel sulfate is far higher than that of ferric sulfate and copper sulfate, carbonaceous organic materials in nickel sulfate are decomposed through high temperature, and therefore the purity of nickel sulfate can be improved to 99% or above through the roasting procedure; and the extraction agent P204 is not needed, and environmental pollution is greatly reduced.