Abstract: ZL702A samples were prepared at cooling rates of 15, 17, 37 and 104 K/s by gravity casting of copper molds with different inner cavity sizes(40, 30, 20 and 10 mm).The microstructure was analyzed by optical microscope and scanning electron microscope, and the tensile mechanical properties were tested at the same time.The results show that with the increase of cooling rate, α-Al grain size gradually decreases from 167.5 μm to 58.3 μm;secondary dendrite arm spacing drops from 19.4 μm to 13.8 μm.The dendrites are significantly refined.With the cooling rate from 15 K/s to 104 K/s, the average tensile strength at room temperature increases by 5%and the average elongation after fracture increases by 14.6%; the average tensile strength at high temperature increases by 18.0%, and the average elongation after fracture increases by 42.9%.In addition, the α-Al grain size has a great influence on the tensile strength of the material at room temperature, while the secondary dendrite arm spacing has a great influence on the high temperature tensile properties of the material.As the cooling rate increases, the supercooling degree increases, the nucleation rate of the alloy during solidification increases, and the α-Al grains and their structures are refined, thereby achieving the purpose of simultaneously improving the strength and toughness of the casting.