In synchrotrons, the high-frequency ripple error of magnet excitation current causes magnetic field ripple, which leads to decreased beam acceptance. The low-frequency tracking error of the excitation current would affect the matching degree of magnetic field and beam energy, which would cause the closed orbit distortion of the beam. The correlation between magnetic field ripple and excitation current ripple of HIAF BRing dipole magnet is studied in this paper. The current quality quantification methods based on high and low-frequency separation are proposed, which evaluate the effect of excitation current error on the beam. The low-frequency tracking error and high-frequency ripple error of the excitation current are obtained by Gaussian smoothing. Three times the standard deviation is used as the quantification indicator of the excitation current in terms of ripple and tracking error. Since parameters of the low-pass filter are determined by the response relationship between magnetic field ripple and excitation current ripple, this method could accurately quantify the magnetic field ripple. Th current tracking error waveform could be used to adjust the reference waveform of synchrotron pulse power supplies, improving the matching degree of magnetic field and beam energy.