The simulation,aimed to detect the quantitative impact of soil water conditions on the acidification of acid sulfate soil (ASS),was held with 8 treatments.The results indicated that water was an important dynamic mechanism on the change of different forms of acid such as exchangeable H⁺,exchangeable Al³⁺,total exchangeable acidity,total sulfuric acidity,total actual acidity,and total potential acidity in ASS.As a result,the changes of water condition would regulate the change of soil acid content.The results also showed that wet but not inundated or over dried ASS was benefit to the formation of exchangeable acidity and total actual acidity.In the treatments of alternation between inundated and drained off,significant acidification happened during the period of aeration drying after drainage,especially at the surface layer of the soil columns.During the inundated periods,the acid forms were relatively stable.The acidity of ASS was discharged in the drainage processes,and the more frequent the altermation was,the larger the total accumulative output and discharge of acidity was.