Abstract: Creep experiments for In783 alloy uniaxial tensile samples were carried out at 620 ℃ and different stress levels, and Norton-Bailey constitutive parameters of the alloy were obtained. The effects of stress levels on creep property and creep mechanism were studied, and the dislocation features of the alloy at typical stress levels were observed. The results show that the Norton constitutive parameters of the alloy at different stress levels were not same. Norton stress index at low stress area was lower than that at high stress area. The creep curves could be well described by Norton-Bailey constitutive equation at low stress area, but can not be accurately described at high stress area. The essential reason for the variation of constitutive parameters was the different creep mechanism in these two stress areas. Creep mechanism was mainly dislocation around the second phase particles at high stress area, and might be dislocation thermal activation climb at low stress area.