This study investigates the microstructure and mechanical properties of a CoCr2Ni3.5VAl1.5Ti high entropy alloy (HEA) annealed at 500 °C, 700 °C, 900 °C and 1100 °C for 6 h. The alloy was prepared using a vacuum induction melting furnace and annealed at the specified temperatures for 6 h. It was then characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). The results indicate that with increasing annealing temperature, the alloy's phase structure transitions gradually from multiphase (fcc, bcc, hcp) to predominantly fcc phase, with relatively stable elemental distributions. Annealing at 500 °C–900 °C mainly strengthens the alloy through precipitates and dislocation strengthening, whereas at 1100 °C, strengthening occurs through grain boundary strengthening and precipitate growth, enhancing the material's strength and ductility. The alloy exhibits optimal comprehensive performance after annealing at 1100 °C. This study provides important insights for optimizing the heat treatment process of HEAs.