Abstract: Sinusoidal waveform of magnetic flux is needed to obtain high-exactitude AC properties measurement results of soft magnets. A new mode to achieve the condition by digital feedback of harmonic compensation was introduced, the waveform of magnetic.flux was analyzed, and the harmonic content in the wave was obtained. The waveform with the same altitude and opposite phase to the harmonic was supplied to the waveform-framing unit, and then the harmonic in output wave was counteracted. Measurement results of electrical steels showed that, after feedback, even at a peak value of induction up to 1.87 T, the form factor fulfilled the condition.