The invention discloses a method for preparing large particle ammonium sulfate from ardealite. The method comprises the steps of firstly adding water into ammonium sulfate generated by conversion of ardealite, ammonia gas and carbon dioxide according to certain proportion and mixing, after heating and dissolving through stirring, adding coal ash and white carbon black for purifying the ammonium sulfate solution, filtering the solution, standing the filtrate for a while, then evaporating and concentrating the filtrate, stopping heating when the density of the concentrated solution is 1.20-1.36g / cm<3>, transferring the concentrated solution to a 80-96 DEG C crystallizing tank, beginning stirring, after the temperature is constant, adding a crystallizing modifier, preserving heat for 20-40 minutes, then adding ammonium sulfate seed crystal, beginning programmed freezing when the seed crystal is not dissolved completely, stopping cooling when cooling to be 30-42 DEG C, filtering, and stoving so as to obtain large particle ammonium sulfate crystal product. The ammonium sulfate product prepared by the method has high purity, good chroma, and large particle, and is not easy to cake; in addition, the preparation method is simple in technological processes, low in production cost, and easy to realize industrialization.