A message synchronization demarcation method includes: a backup board receives a message of an opposite terminal from an interface board; the message is copied to a main board; the main board processes the message, copies it to the backup board through the buffer unit and transmits the data. Also a message synchronization demarcation system is provided. The data backup between the main board and the backup board is performed through the buffer area without occupying the transport layer resource, so the data flux of communication channels is reduced, the payload is lowered, and the backup steps of messages between the main board and the backup board is simplified. Using the present disclosure, the received message can be demarcated, and the accuracy of message transmission is further improved.