Method and device for automatically adjusting impedance

The invention provides a method and a device for automatically adjusting an impedance, wherein the method relates to an access device. The invention is characterized in that: a plurality of groups of operational parameters of a user interface chip are stored on the access device; each group of operational parameters corresponds to one impedance of the access device; and the method comprises a step 1 of determining one group of operational parameters from a plurality of groups of operational parameters of the user interface chip to allocate the user interface chip, a step 2 of sending a signal to a circuit by the user interface chip, a step 3 of receiving a return signal of the signal by the user interface chip, and a step 4 of utilizing the signal and the return signal of the signal to calculate a return loss, calculating a difference value of the return loss and an ideal return loss and using the access device to adjust the impedance according to the difference value. The invention sufficiently considers the