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The solidification process of polycrystalline nickel base superalloy can effectively reduce the porosity defects. The microstructure and mechanical properties of K417G alloy were studied at four different pouring temperatures of 1360 ℃, 1380 ℃, 1400 ℃ and 1420 ℃. The results show that with the increase of pouring temperature, the porosity decreased significantly, the γ" phase size and the (γ+γ") eutectic content increased slightly, while the MC carbide is not obvious. The overall mechanical properties at 1360 ℃ are significantly lower, the tensile strength and elongation of at 900℃, 10-3s-1 are only 656 MPa and 4.2 %, respectively, and the stress rupture life at 760 ℃ / 645 MPa is only 18 h. At 1380 ℃ to 1420 ℃, the difference of tensile properties at 900 ℃, 10-3s-1 is relatively small, and the average tensile strength and elongation are 761 MPa and 5.7 %, respectively, while the stress rupture property at 760 ℃ / 645 MPa tends to decline with increasing temperature. The stress rupture life of 1380 ℃, 1400 ℃ and 1420 ℃ are 88 h, 80 h and 74 h, respectively.