Objective:: This study is aimed at measuring the ripple of magnetic power supply of BEPCII and checking its effect to beam energy. Materials and methods:: A sensor made of printed circuit board coils is designed and manufactured. The sensor was inserted into a good area region of the magnetic field with the surface perpendicular to the field force lines. The change of the magnetic field would be detected according to Faraday’s law. Results:: The experiment result indicates that the time-dependent ripple of the magnetic field is in the magnitude of ppm. Conclusion:: Such a small effect of the time-dependent ripplecan be negligibleto beam energy.