The high-temperature stress rupture properties of K417G superalloy with various Mn contents (0.09wt%~0.35wt%) were studied and the existence form and distribution of Mn were evaluated as well. The results show that Mn is solid-dissolved in γ matrix and enriched in γ'-depleted matrix in front of γ+γ' eutectic cap. Mn elements promote the segregation of Al and Ti to interdendrite zone, thus increasing the volume fraction of γ+γ' eutectic in interdendrite zone and decreasing the size of γ' phase in dendrite core. With the increase of Mn content, the stress rupture life and the plasticity decrease greatly under the condition of 950 °C/235 MPa. The alloy with the minimal Mn content shows the optimal high-temperature stress rupture properties.