A computer peripheral device, which is adapted to a computer system having a system-end connecting interface, includes a device-end connecting interface, an impedance unit and a control unit. The device-end connecting interface includes a power pin and a ground drain pin. The power pin electrically connects to a power source of the computer system and generates a voltage level on the ground drain pin. The impedance unit electrically connects to the power pin and ground drain pin of the device-end connecting interface respectively and decreases the voltage level of the ground drain pin optionally. The control unit electrically connects to the ground drain pin of the device-end connecting interface and determines a USB specification of the system-end connecting interface according to the voltage level of the ground drain pin.