Abstract: To address the problem that the thermal voltage converter (TVC) is unable to achieve the AC-DC conversion of ultra-low frequency voltages, an AC-DC transfer method is proposed with using dual-heater TVC based on the square characteristics of the output thermoelectric potential of the TVC and the square sum identity characteristics of two quadrature sinusoidal signals with identical amplitude. The ultra-low frequency voltage below 10 Hz is traced to the DC voltage standard. The ultra-low frequency voltage AC-DC transfer system is developed. The standard uncertainty of AC-DC transfer results at 10 Hz does not exceed 14 µV/V. A verification experiment is developed by comparing the AC-DC transfer results that from dual-heater TVC and planar multijunction thermal converter (PMJTC). The AC-DC transfer results obtained by the two different methods are consistent and the inconsistency is within the uncertainty range.