Amorphous structure of the melt-spun Cu50Zr50 amorphous alloy ribbons were confirmed by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM). Isothermal crystallization kinetics of these alloy ribbons were investigated using differential scanning calorimetry (DSC). Besides, Arrhenius and Johnson-Mehl-Avrami (JMA) equations were utilized to obtain the isothermal crystallization kinetic parameters. As shown in the results, the local activation energy Eα decreases by a large margin at the crystallized volume fraction α<0.1, which proves that crystallization process is increasingly easy. In addition, the local activation energy Eα is basically constant at 0.1<α<0.9. Therefore, it turns out that the unchanged barrier is overcome in the crystallization process. Finally, Eα rapidly decreases at 0.9<α<1, implying that crystallization becomes easier and easier to proceed. Nucleation activation energy Enucleation is greater than growth activation energy Egrowth, so nucleation is harder than growth in isothermal process. In terms of the local Avrami exponent n(α), it ranges 1.1–7.4, revealing that isothermal crystallization mechanism is interface-controlled one- two- or three-dimensional growth with different nucleation rates.