Abstract: This invention discloses an automatically signal-tuning system for using in video signal transmission. The system can use the auto-tuning function in video transmission circuit to make the system automatically detect the extents of frequency loss and delay affected by a transmitting cable and to adjust the received signal to approximate to the original transmitted signal once system reboot and/or transmitting cable hot-plugging. The compensation for the signal frequency loss and the signal delay is by comparing and analyzing the attenuation and the delay values to provide the video signal on the transmitting cable to be automatically adjusted to the optimized response value.