The present invention provides a chip-to-chip signal transmission system. Signal transmission is performed between a transmitter of a first chip and a receiver of a second chip through a transmission-metal-pad and a reception-metal-pad. When receiving a driving-testing signal, the transmitter transmits a transmission-testing-coupling signal through the transmission-metal-pad according to the driving-testing signal. A receiving-testing circuit on the first chip receives the transmission-testing-coupling signal through the transmission-testing-metal-pad, and outputs a transmission-testing signal according to the transmission-testing-coupling signal. When receiving the driving-testing signal, a driving-testing circuit on the second chip transmits a receiving-testing-coupling signal through a reception-testing-metal-pad according to the driving-testing signal. The receiver receives the receiving-testing-coupling signal through the reception-metal-pad and outputs a receiving-testing signal according to the receiving-testing-coupling signal.