Abstract: Embodiments of the present invention provide a data transmission method and device, which are to be applied to a source client, wherein the source client is a client in a foreground running status in a mobile terminal, the mobile terminal, by means of a split-screen function, divides the display screen thereof into a first split screen for displaying a running interface of the source client and a second split screen for displaying a running interface of a target client, the target client is a client in a foreground running status in the mobile terminal. The method comprises: establishing a communication connection between the source client and the target client; receiving a drag instruction for a thumbnail of target data in the source client and moving the thumbnail according to the drag instruction; monitoring whether a data transmission instruction for the target data is received, if yes, transmitting the target data to the target client through the established communication connection.