A serial data transmission system, includes a transmitting terminal for transmitting a data, a receiving terminal for receiving the data transmitted by the transmitting terminal, a first connecting capacitor connected between the transmitting terminal and the receiving terminal, and a second connecting capacitor connected between the transmitting terminal and the receiving terminal, wherein the transmitting terminal comprises a transmitting terminal driver unit and an amplitude detection unit connected with the transmitting terminal driver unit, the transmitting terminal driver unit outputs a pair of differential signals, the amplitude detection unit detects an amplitude variation of the differential signals output by the transmitting terminal driver unit, and outputs an indication signal indicating whether the transmitting terminal and the receiving terminal are properly connected with each other. A serial data transmission method is further provided.