Stress rupture test at 975℃/196MPa and room temperature tensile test were conducted in standard heat-treated K424 alloy after overheating at different conditions (1050℃~1150℃/2h, air cooling), the characterization of microstructures and fracture features were then investigated. The results showed that mechanical properties of standard heat-treated K424 alloy were only slightly lower after overheating at 1050℃~1150℃ for 2h, the mechanical property indexes were obviously higher than the values in standard. Microstructural characterization indicated that grain morphology, grain boundary morphology and γ’ phase in the interdendritic regions showed no significant change after overheating at different conditions. The more cuboidal primary γ’ phase and the precipitation of secondary γ’ phase in γ channel were responsible for the slightly diminished mechanical properties after overheating. In addition, the high temperature and room temperature fracture mechanisms of overheated K424 alloy were also discussed.