The invention discloses a method and a system for realizing instant message and short message/multimedia message intercommunication. The method comprises that: the message/multimedia message center obtains virtual MSC addresses from HLR when the message/multimedia center needs to send the short message/multimedia message, and transmits a first short message/ multimedia message sending request to a virtual MSC, a virtual MSC forwards the first short message/ multimedia message transmission request to an instant message server through an open interface; and the instant message server transmits the short message/ multimedia message to a corresponding messaging client according to the client number of a reception terminal carried in the first short message/ multimedia message. The invention searches the address through the virtual MSC short message and realizes the fact that the mobile terminal transmits the short message/ multimedia message to the instant messaging application.