The invention discloses a green method for preparing battery grade nickel sulfate from nickel salt. The green method for preparing battery grade nickel sulfate from the nickel salt comprises the stepsthat the nickel salt and ammonium salt are mixed, ammonia water is added, ammonia leaching reaction is carried out, a first-stage ammonia leaching solution and first-stage ammonia leaching residues are obtained through solid-liquid separation, the first-stage ammonia leaching solution is subjected to ammonia distillation, the pH of the solution obtained after ammonia distillation is adjusted, then nickel powder is prepared through adopting a pressurized hydrogen reduction method; filtrate obtained by carrying out multi-stage ammonia leaching reaction and solid-liquid separation on the first-stage ammonia leaching residues returns to first-stage ammonia leaching slurrying, filter residues is washed by using a three-stage CCD, then a carbonization process is adopted, CO2 partial pressure, reaction time and reaction temperature are controlled, a carbonized liquid and carbonized residues are obtained, and pyrolysis and calcination on the carbonized liquid are carried out, then a magnesiumoxide product is obtained; and the carbide residues are subjected to reduction smelting through a pyrogenic process, and upper-layer rich-manganous slags and lower-layer nickel-cobalt-manganese slagsare obtained after crushing and screening. According to the green method for preparing battery grade nickel sulfate from the nickel salt, the method is easy to control, green and energy-saving, the ammonia water and the ammonium salt in the system can be recycled, a new process for preparing battery grade nickel sulfate without wastewater, waste residues and extraction is realized, and the production cost is greatly reduced.