The effects of increasing Al and decreasing Nb on microstructure and mechanical properties of GH706 alloy before and after long time age heat treat were studied. Result show that increasing Al content and decreasing Nb content in alloy contribute to disappear of γ′′、Laves and δ phases in alloy, and after aged at 750℃ for 500h, γ′ and η grow up slightly and mechanical properties reduce limited. While precipitates of alloy without modification(conventional GH706) grow up rapidly and mechanical properties decrease obviously. The result indicated that the alloy can be used at higher temperature with modification of increasing Al and decreasing Nb.