An AC-DC transfer standard(TS) is used for the AC voltage standard in the range of 2 mV to 1000 V below 1 MHz. Micro-potentiometer(${mu}Pot$) is used to evaluate the ac-dc transfer difference(ADD) of the TS below 200 mV range. The ADD of the TS were changed by the loading effect caused from the input impedance change of the TS depend on frequency. An input impedance evaluation technique of the TS using ${mu}Pot$ has been developed.