Abstract: AlCoCrFeNi_2.1 eutectic high entropy alloy underwent a 30% cold rolling process, followed by annealing treatments at 500 ℃, 700 ℃, and 900 ℃ for 1 h，respectively. A systematic study was conducted on the microstructure and mechanical properties of the alloy under hot rolling and different temperature annealing conditions. The results show that there are three types of microstructure in the as-cast AlCoCrFeNi_2.1 alloy: lamellar eutectic, irregular eutectic, and hypereutectic. The annealing heat treatment has little effect on the types, morphology, and size of the microstructures in the AlCoCrFeNi_2.1 sample. The cold rolled sample has higher microhardness and strength compared with that of the as-cast sample. With the increase of heat treatment temperature, the geometrically necessary dislocation density of the alloy decreases, resulting in a reduction in microhardness and strength, while the elongation is improved. The dislocation strengthening and heterogeneous deformation induced stress strengthening are the two primary strengthening mechanisms of AlCoCrFeNi_2.1 alloy sample before and after cold rolling and heat treatment.