The invention discloses a peer-to-peer (P2P) flow recognizing method and device. The method comprises the steps of: receiving a TCP (Transmission Control Protocol) message of a source or destination node as a local node, judging whether the message is a conversation first message and is in an entering direction, if yes, judging whether the information of the destination node of the message exists in a P2P node list, if yes, marking the local conversation as the P2P conversation, if not, recognizing the message by adopting a preset P2P flow recognizing method, if the message is recognized to adopt the P2P flow, marking the local conversation as the P2P conversation, and adding the information of the destination node of the message into the P2P node list; and if the message does not adopt the P2P flow, judging whether the conversation is marked as the P2P conversation, if not, recognizing the message by adopting the preset P2P flow recognizing method, if the message is recognized to adopt the P2P flow, judging whether the direction of the local conversation is the entering direction, if yes, marking the local conversation as the P2P conversation, and adding the information of the destination node of the first message of the local conversation into the P2P node list. The invention accelerates the recognition of the P2P flow.