The invention discloses a process for producing high-purity ammonium lignin by taking papermaking black liquid as material. The process comprises the following steps: firstly, precipitating the papermaking black liquid by acetic acid, centrifugally separating the papermaking black liquid to obtain sediment crude lignin, and washing the crude lignin into a neutral state by water, carrying out ammonium reaction on the crude lignin, a certain amount of ammonia water and hydrogen peroxide for a period of time under a certain temperature condition, centrifuging reaction liquid after reaction, and spray drying upper clear liquid to obtain the ammonium lignin. The obtained ammonium lignin has high purity and good water-solubility, does not contain metal elements, such as sodium, calcium and silicon which are usually contained in the papermaking black liquid, and can be widely used as biomass fuel or fuel additive.