Abstract: A system and method for changing communication channels is provided. In the system, a transmitting peer divides transmission data into frames to generate an unfinished frame list and transmits a data frame to a receiving terminal according to the unfinished frame list and a receiving peer receives a data frame from the transmitting peer and transmits a response frame to the transmitting peer in response to the received data frame during direct channel communication. The transmitting peer transmits incompletely transmitted data frames (whose response frames have not been received) included in the unfinished frame list to the receiving peer through a relay server when a communication scheme has been changed from the direct channel communication scheme to a relay channel communication scheme.