Abstract: That any minimum merge dependency set belonging to the set of FD F has the same properties when some minimum merge dependency set belonging to the set of FD F has some properties is discussed.And then the concepts of generalized left side conflict and generalized right conflict of the set of FD F are given.The full and necessary condition under which a database schema without inside conflict can be decomposed into one meeting P 3 and without α cycle, and the necessary condition under which a database schema with inside conflict can be decomposed into one meeting P 3 and without α cycle are given and proved.