Data transmission method, device and system

The invention provides a data transmission method, device and system, and relates to the field of data transmission. The data transmission device dynamically determines the transmission frequency according to the residual flow and the residual transmission time, determines whether the residual flow is sufficient or not by comparing the residual flow with a transmission frequency threshold value, and searches other data transmission devices with sufficient residual flow in the local area network if the residual flow is insufficient. And the data is transmitted to the other data transmission device through the local area network, the transmission process does not consume data flow, and the other data transmission device transmits the data to the external target equipment. Therefore, under the condition that the residual flow is insufficient, the data transmission device with sufficient residual flow in the local area network is discovered and used for data transmission, so that the excess flow cost is reduced,