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An investigation was carried out to study the effects of γ’ formation and strengthening elements (At, Ti and Ta) on the microstructure and stress rupture properties of nickel base single crystal super-alloys. The results show that with the increase of γ’ formation and strengthening elements, the percentage of γ-γ’ eutectic and the misfit degree of γ/γ’ increases. Detailed microstructural analysis revealed that with the increase of γ’ forming element content, the morphology of γ’ changed from spherical to cubic, then irregular shape; and the size of γ’ increases gradually. Excessive γ’ formation and strengthening elements will lead to the precipitation of μ phase during stress rupture tests. The alloy with 5wt.%AI, 1wt.%Ti and 6wt.%Ta has the best stress rupture property.