Abstract: Keeping the total amount (3.12at%) of γ' phase forming elements (Ta+Ti) in the nickel-based superalloy unchanged, the as-cast structure of different Ta/(Ta+Ti) alloys were studied by using optical microscope, scanning electron microscope, electron probe micro-analyzer, differential scanning calorimetry, and J MatPro software.The primary dendrites arm spacing (λ₁), the secondary dendrites arm spacing (λ₂), the average size and volume fraction of γ' phase and the segregation behavior of elements were analyzed, and the changes of solidus temperature (T_S), liquidus temperature (T_L), γ' solution temperature (T_γ') and hardness of the alloys were investigated.The results show that the morphologies of the γ' phase changes from spherical to cubic with the increase of Ta/(Ta+Ti). The λ₁, λ₂ and the average size and volume fraction of γ' phase are increased first and then decreased. The difference in the size of the γ' phase between the interdendrites and dendrites is decreased. With the increase of Ta/(Ta +Ti), the segregation of W element is reduced, and the hardness and average hardness between interdendrites and dendrites are increased. The solidification temperature range of the alloys decreases with the increase of Ta/ (Ta+Ti), and the solid solution temperature of the γ' phase increases, leading to the enhancement of the stability of γ' phase.