The LOX (liquid oxygen)/kerosene rocket engine is widely used in heavy launch vehicles owing to its low cost, high performance, and high reliability. However, the next-generation LOX/kerosene rocket engine requires a new superalloy that can resist oxygen-rich combustion. The K4061 alloy is a second-generation superalloy that has better resistance to oxygen-rich combustion compared to the first-generation superalloy due to the addition of the Cu element in its composition. However, there is limited research on the role of the Cu element in the superalloy. This study investigates the effect of Cu content (mass fraction) ranging from 1% to 10% on the microstructure and Cu distribution of K4061 alloy using thermodynamic calculations along with DSC, SEM, and TEM experiments. The results show that during the equilibrium solidification of K4061 alloy, the γ matrix precipitates first, followed by precipitating MC carbides at the end of solidification. The addition of Cu does not affect the equilibrium solidification path of the alloy; however, it lowers the solidus and liquidus temperatures of the alloy and the precipitation temperature of MC. During the nonequilibrium solidification, the δ phase is also precipitated at the late solidification stage. The types of precipitated phases of K4061 alloy with different Cu contents remain unchanged, consistent with thermodynamic calculations. However, Cu-rich phases are not found in the sample, and Cu does not dissolve in MC in large quantities or segregate into grain boundaries. TEM results show that Cu is enriched in the strengthening phases, and the size of the strengthening phases slightly increases with the addition of Cu during aging heat treatment. Additionally, the addition of Cu reduced the room temperature and 750°C tensile strength of the alloy.