<p>In this work, the tailoring isothermal crystallization kinetics between the Fe₂₀Co₂₀Ni₂₀Cr₂₀(P_0.45B_0.2C_0.35)₂₀ high-entropy metallic glass (HEMG) and the precursor Fe₇₅Cr₅P₉B₄C₇ metallic glass (MG) by similar solvent elements Co, Ni and Cr substitution of Fe were conducted by phase characterization, Johnson–Mehl–Avrami and Arrhenius approaches. Compared with the precursor Fe₇₅Cr₅P₉B₄C₇ MG, the Fe₂₀Co₂₀Ni₂₀Cr₂₀(P_0.45B_0.2C_0.35)₂₀ HEMG possesses a higher completion time of the entire event and the local activation energy, a smaller Avrami exponent and local Avrami exponent (<i>n</i>(<i>x</i>)) with a crystallization of growth with a reducing nucleation rate and a more complex change tendency of <i>n</i>(<i>x</i>), which corresponds to a more sluggish isothermal crystallization event, implying that the process can be retarded after high-entropy alloying by similar solvent elements Co, Ni and Cr substitution of Fe in Fe₇₅Cr₅P₉B₄C₇ MG. Additionally, both of the alloys possess diverse crystallized products, an improved local activation energy and a complex change tendency of <i>n</i>(<i>x</i>) along with a changeable nucleation rate.</p>