The invention discloses a system and method for remote wide area network disaster recovery backup. The method comprises the steps that when data transmission is conducted on each file data stream, whether a file data stream identical to a current file data stream is transmitted or not is identified by a data storage server on one node; if yes, an index of the current file data stream is directly pointed to the same transmitted file data stream, the current file data stream is deleted, and it is determined that the stored unique file data stream is sent to a data center server; the file data stream obtained is received by the data center server after repeated data deletion is conducted on the data storage sever of one node and is transmitted to a remote site server through a data storage server on the other node; due to the fact that the data storage server searches for and positions the repeated file data streams and it is guaranteed that a large number of data file streams are not transmitted repeatedly, the data transmission amount is reduced, the network bandwidths and the transmission time are saved, and it is guaranteed that backup data do not occupy a large amount of storage space of the remote site server.