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Acid-base dissociation constant,pKa,which defines the ionization degree of organiccompounds,is an important parameter for their toxicity and environmental behaviorand fate.At present there are numerous studies on theoretical prediction of pKa values.In order to compare the performance of different methods in pKa prediction referringto special dissociation groups,we selected three typical methods,which are quantumchemical method（QC）,sophisticated increment method SPARC including MOtheory and fragment-based ACD,and carried out calculation on ca.1200 organic acidsand bases.