Abstract: In this paper the as-cast microstructure, the rules of phase precipitation, the change of microstructure and minor phase content and the degeneration of aluminide coating after thermal exposure at temperature range from 850℃ to 1100℃ for 1000-3000 hours have been studied in comparison between two kinds of low chromium-high tungsten cast nickel-base superalloys.The experimental results have shown that these alloys have high structural stability, the alloys of normal composition did not precipitate TCP phase in all thermal exposure conditions and the total amount of minor phase in K002 and K19H after thermal exposure at 1050℃/1000 hr. only increased by 89%and 18% respectively. The following reactions have been proposed:Because the above reactions pick up residual carbon in γ-matrix, the formation of M6C and M23C6 is restricted.Besides, large quantity of niobium containing in MC carbide of K19H mates MC stabilize, therefore slows down the following reaction