The present disclosure is related to a P2P file transmission system and method, the system according to the present disclosure may include a P2P node managing system managing users connected to the system, and managing P2P file transmissions between the users; and a relay server relaying the file transmitted to the file receiver from the file sender when the P2P file transmission by the direct connection between the file sender and the file receiver fails. According to an embodiment of the present disclosure, the present disclosure provides more stable file transmissions under an unstable environment for the P2P file transmission such as NAT and the P2P file transmission system may be applied to various network places.