MA activity is characterized by intelligent decision process. MA decision is made on the basis of obtaining and estimation of internal and external data. MA decision support system (for short MA DSS) can deal with a plenty of data and information, and imitate the intelligent behavior of the human brain. MA DSS can deal with non-structural and non-linear problem, as well as completely reflect the whole MA activity, so it ensures that the investigation before MA, finishing MA trade and post merger integration is a complete process. The aim of building MA DSS is to change the data into useful information so as to make MA decision, furthermore, to find the general and profound rules (knowledge) and optimize the MA decision, at last to realize the knowledge management of MA decision.