Thermo-Calc （TC）thermodynamic calculation software and TCNI10 professional nickel-based alloy database were used to calculate and analyze the phase transition paths during the equilibrium solidification and cooling process of CW12MW and CW6MC cast nickel-based alloys，as well as the effects of the main alloy elements of these two alloys on the vertical section phase diagrams of equilibrium systems.The results indicate that the phase transition paths during the equilibrium solidification and cooling process of nickel-based alloy CW12MW are respectively： Liquid→Liquid+Austenite→Liquid+Austenite+M

6

C-carbide→Austenite+M

6

C-carbide→Austenite+M

6

C-carbide+Sigma→Austenite+M

6

C-carbide+Sigma+M

23

C

6

-carbide→Austenite+M

6

C-carbide+Sigma+M

23

C

6

-carbide+Mu_phase→Austenite+Sigma+M

23

C

6

-carbide+Mu_phase，the main intermetallic phases precipitated are Sigma phase and Mu phase during equilibrium transition process，and their maximum molar fractions are 0.27 and 0.003 7，respectively，Cr、Mo and W elements mainly promote the formation and stability of Sigma phase and Mu_phase.The phase transition paths during equilibrium solidification and cooling process of cast nickel-based alloy CW6MC are respectively：Liquid→Liquid+Austenite→Liquid+Austenite+γ′-Ni

3

（Al，Ti）→Austenite+γ′-Ni

3

（Al，Ti）→Austenite+γ′-Ni

3

（Al，Ti）+Sigma→Austenite+γ′-Ni

3

（Al，Ti）+Sigma+δ-Ni

3

Nb→Austenite+γ′-Ni

3

（Al，Ti）+Sigma+δ-Ni

3

Nb+M

23

C

6

-carbide→Austenite+Sigma+δ-Ni

3

Nb+M

23

C

6

-carbide→Austenite+Sigma+δ-Ni

3

Nb+M

23

C

6

-carbide+P_phase→Austenite+δ-Ni

3

Nb+M

23

C

6

-carbide+P_phase，the main precipitated intermetallic phases are Sigma phase and P_phase during equilibrium transition process， and their maximum phase molar fractions are as high as 0.17 and 0.25， respectively. The increase of Mo content is beneficial to the formation and stability of Sigma phase， and the increase of Nb content mainly promotes the precipitation tendency of δ-Ni

3

Nb phase.The results of theoretical calculation and production practice show that the optimum solution temperatures of casting nickel-based alloy CW12MW and CW6MC are （1 230±14）℃ and （1 200±14）℃，respectively.