The invention relates to a method for local area network positioning in instantaneous network data transmission. The method includes the steps: a), connecting clients; b), recording client information, client IDs (identities), client intranet IPs (internet protocols) and ports and client public network IPs and ports by a server; c), acquiring related information of a target client; d) positioning and judging local area networks; e), if a source client and the target client are in the same local area network, performing direct data transmission; and f), if the source client and the target client are not in the same local area network, adopting an existing data transmission method. According to the method, a sender and a receiver in data transmission are judged whether in the same local area network or not, and then different transmission schemes are adopted according to judgment; if the sender and the receiver are in the same local area network, data is transmitted through the local area network without occupying bandwidth of a public network, so that network resources are saved; meanwhile, by the aid of bandwidth advantages inside the local area network, instantaneity of data transmission is guaranteed, and quality requirements of data transmission are met.