A detection circuit and a wake-up method are provided. The detection circuit is adapted to a high definition multimedia interface (HDMI) receiver that enters a power-saving mode in a fixed rate link (FRL) mode to detect whether or not an HDMI transmitter starts to transmit video packets through the FRL. The detection circuit includes a signal detection circuit detecting whether or not signal exists on the FRL and an FRL packet determination circuit determining whether or not the FRL packets are the video packets according to a variable value characteristic of the video packets and/or a fixed value characteristic of gap packets. An existence of the signal on the FRL indicates an existence of FRL packets on the FRL. When the FRL packets are the video packets, the FRL packet determination circuit wakes the HDMI receiver from the power-saving mode to resolve the video packets and display videos.