Overturning the traditional alloy design concept, high-entropy alloys (HEAs) or media-entropy alloys (MEAs) are currently drawing widespread attentions from the materials science community, particularly those with a single phase of face-centered cubic (fcc) crystal structure, due to their superior properties, such as large elongation, good corrosion resistance and exceptional fracture toughness etc. In present work, A new MEA with a nominal composition of 66.66Co-16.67Cr-16.67V (at. %) was designed, which possess single fcc structure after solid solution treated at 1473 K for 2 h. To modify the microstructure, the initial alloy was cold-rolled to a thickness reduction of 70 %, and then heated treated at different temperatures (1000 ºC, 1100 ºC and 1200 ºC) to obtain different microstructures. The recrystallisation behavior and mechanical properties were studied by in-situ synchrotron XRD diffraction, electron back scatter diffraction (EBSD), and transmission electron microscopy (TEM). The results showed that this alloy can undergo phase transformation under thermal treatment or subjected to plastic deformation, thereby significantly affecting the microstructure and mechanical properties.