The effects of Ru on the as-cast, heat-treated microstructures and stress rupture properties under 1100-1150 ℃ were investigated in new generation Ni-based single crystal superalloys DD22 with two levels of Ru (0% and 2%, mass fraction) additions. The results indicate that the addition of Ru results in the decrease of the solidus and liquidus temperatures, the volume fraction of (γ+γ') eutectic as well as solidification segregation. The size of γ' phase and elemental partitioning ratio of Re and Cr which are important for the precipitation of TCP phase decreases after heat treatment with Ru addition. Ru addition decreases the size of γ' phase, increases γ/γ' misfit and solution strengthening effect and inhibits the precipitation of TCP phase in the process of stress rupture loading, which finally improve the stress rupture properties of DD22 alloy significantly.