The invention discloses a bidirectional relay system power distribution method based on an AF (Amplify-and-Forward) mechanism, which is suitable for a bidirectional relay system based on the AF mechanism. According to the method, the system QoS (Quality of Service) requirement and transmitter peak transmitting power limit are taken as constraint conditions, and the target is to minimize the system total transmitting power. The transmitting power of a transmitter is dynamically adjusted by means of a channel statistical value according to the requirement of a source node on the data rate, so that the system total transmitting power is minimized under the condition that the system QoS requirement and the transmitter peak transmitting power limiting condition are met.