A universal serial bus (USB) signal transmission device, an operation method thereof, and a USB cable are provided. The USB signal transmission device includes a signal processing circuit, a switch circuit, and a control circuit. A first terminal of the switch circuit is coupled to a first USB circuit. A second terminal of the switch circuit is coupled to a second USB circuit. The control circuit turns off the switch circuit during a detection period to detect both terminals of the switch circuit to obtain a detection result. The control circuit turns on the switch circuit during a transmission period, and controls a transmission direction of the signal processing circuit according to the detection result.