The influence of thermal shock behavior between 960 degrees C and room temperature on microstructure and tensile properties of IN718 alloy after three heat treatments was investigated in this paper. The experiments show that protective and dense oxide films with the composition of Cr2O3, Ti0.95Nb0.95O4 and (Cr, Fe)(2)O-3 are formed on the surface of alloys. The average oxide films increased with the thermal shock cycle. The thermal shock behavior changed the distribution and quantities of delta phases, which have significantly reduced the strength and increased the elongation of IN718 alloy. The decrease of strength was mainly determined by the dissolution of strengthening phase and grain coarsening. High standard treatment alloy shows the best thermal shock resistance since the strength decreased smallest after thermal shock.