A communication transmission system is applied to an application device and includes a power detection circuit, and a radio frequency module. The power detection circuit is used for detecting the power on the output port of the communication transmission system, and for producing a feedback signal. The radio frequency module is connected to the power detection circuit for receiving the feedback signal so as to adjust its output power. In addition, the power detection circuit is built to be independent of the RF module for directly detecting the power on the output port of the communication transmission system which represents the actual power of the application device, thereby achieving the purpose of outputting a more stable and accurate output power through the RF module.