The invention relates to a method for preparing 
ammonium sulfate by continuous conversion of phosphogyspum with a polycrystalline method, belonging to the technical fields of resource comprehensive utilization and 
chemical industry, and relates to a method for producing 
ammonium sulfate by conversion of phosphogyspum with a polycrystalline method based on a byproduct phosphogyspum in a (
sulfuric acid) wet 
phosphoric acid industry as a main 
raw material. The production process comprises the following steps: (1) pretreating the 
raw material of phosphogyspum discharged in the wet phosphoric acidindustry so as to obtain purified phosphogyspum; (2) absorbing 
ammonia and 
carbon dioxide with a 
ammonia-
sulfate-containing primary 
lotion which is produced by washing a 
calcium carbonate filter cakewith water in a 
filtration process in a 
carbonation tower so as to produce an 
ammonia sulfate and 
carbonate solution; (3) connecting a 
calcium carbonate polycrystalline 
nucleus generator with a multiple-tank or multiple-partition groove type reactor with a stirrer in series to constitute a conversion crystallizer; (4) filtering a reaction material 
slurry discharged from the conversion crystallizer so as to obtain a 
filter cake and filtrate containing 38-40% by weight of 
ammonium sulfate; (5) carrying out secondary countercurrent washing on the 
filter cake obtained in the step (4) with clear water, and feeding the ammonia-sulfate-containing primary 
lotion to the 
carbonation tower for absorbing gas ammonia and 
carbon dioxide so as to produce an ammonia sulfate and carbonate liquid; and (6) neutralizing and decarburizing the filtrate containing 
ammonium sulfate from the step (4) with 
sulfuric acid, then centrifugally separating so as to obtain a 
crystal containing wet 
ammonium sulfate, separating out a mother liquid, carrying out cycle concentration on the mother liquid, and 
drying the 
crystal containing wet 
ammonium sulfate so as to obtain a finished product ammonium sulfate.