Abstract <p>Spin-frustrated Ca₃Co_2-<i>x</i>Fe_<i>x</i>O₆ (<i>x</i> = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) compounds were successfully synthesized. Their magnetization and magnetodielectric coupling properties were investigated in detail. With Fe substitution, the subtle magnetic structure can be modified effectively, and the three magnetization steps are inhibited gradually. The <i>ac</i> magnetic susceptibility of Ca₃Co_2-<i>x</i>Fe_<i>x</i>O₆ exhibits typical frequency-dependent behavior, implying metastable magnetization. Due to the suppression effect of Fe on magnetic frustration and intrachain ferromagnetic interaction, the thermal relaxation of the short-range magnetic correlation decelerates. The two obvious dielectric anomalies in temperature-dependent dielectric permittivity around <i>T</i>_<i>C</i> and <i>T</i>_<i>f</i> also vanish as <i>x</i> ≥ 0.08, confirming the influence of the variation of subtle magnetic structure on the dielectric property of Ca₃Co_2-<i>x</i>Fe_<i>x</i>O₆ compounds. The same sign of Δ<i>ε</i> and Δtan<i>δ</i> in magnetic dependent dielectric measurement indicates that the observed magnetodielectric effect in Ca₃Co_2-<i>x</i>Fe_<i>x</i>O₆ is mainly contributed by the reorientation of the dipoles.</p> Graphical abstract <p></p>