Abstract: <FONT face=Verdana>In the existing production of caprolactam，there are some qualitative problems about by-product ammonium sulfate,such as uneven crystal size,bad color and morphology.In order to get better products,the evaporation crystallization process of ammonium sulfate solution obtained by caprolactam synthesis neutralized liquid was studied and optimized systematically .The effects of parameters,such as seeds added,agitation speed,evaporation temperature,and pH of solution,on the crystallization process,product size distribution,and crystal quality were investigated.And the optimal operation conditions of crystallization were determined.The products were improved in terms of crystal size,color,and purity under the optimized operation conditions,which will,give valuable guidance to the industrial process. <BR></FONT>