High-entropy alloy (HEA) microfibers exhibit promising prospects in microscale high-tech applications due to their exceptional mechanical properties and stability. However, the strength-plasticity tradeoff largely hinders their further industrial applications. Heat treatment can optimize the mechanical properties of HEA microfibers. However, the traditional heat treatment (CHT) faces challenges in accurately adjusting the microstructures in a short period of time, while also being prone to grain coarsening, which can affect performance. In this study, an electric current treatment (ECT) technique is used to finely modulate the properties of cold-drawn CoCrFeNi high-entropy alloy microfibers on a microscale (~70 μm in diameter), the effects of thermal and athermal effects during ECT on microstructure and mechanical properties are systematically investigated through electron back scatter diffraction, transmission electron microscopy, and synchrotron radiation. A model of recrystallization, nucleation and growth of HEA microfibers is established. Compared with CHT, the synergistic effects of electron wind force and Joule heating during ECT significantly accelerate recrystallization kinetics, yielding finer and more homogeneous grains with a great decrease in dislocation density, and finally lead to better mechanical properties. The ECT-processed HEA microfibers achieve a yield strength in a range from 400 to 2033 MPa and a tensile elongation reaching 53%, which are much higher than those of CHT samples. These results demonstrate that the ECT is effective for optimizing the microstructure and properties of HEA microfibers, and can also provide both a theoretical foundation and technical guidance for fabricating high-performance metallic microfibers.