The invention relates cross-terminal input method, apparatus and system. In certain embodiments, the method includes sending a request by a first terminal device to a server to acquire a transmission channel, when a triggering event is detected at the first terminal device; receiving interface information of the transmission channel from the server; repeatedly acquiring data transmitted from the server according to the interface information of the transmission channel; and updating output according to the acquired data. The cross-terminal input system includes first and second terminal devices. The first terminal device sends a request to a server to acquire a transmission channel, and receives interface information of the transmission channel. The second terminal device acquires the interface information, and uploads user input data to the transmission channel accordingly. Then, the first terminal device receives the user input data, and updates output with the received data.