Abstract: A method of monitoring data transmission is applied to a data transmission system which includes at least one server device and a client device, each of which is linked to a telecommunications network. The at least one server device is used for generating a data stream and a data generation rate relative to the data stream. The data stream and the data generation rate are transmitted to the client device over the telecommunications network. The client device calculates a data receiving rate of data received from the data stream by the client device, and determines whether a comparison result of the data receiving rate with the data generation rate meets a predetermined condition. If YES, the client device generates a warming signal.