The deformation microstructures, deformation behavior and mechanisms of FGH98 after tensile tests at room temperature(23℃) and intermediate temperatures(650℃、750℃、815℃)have been investigated by scanning electron microscopy(SEM)and transmission electron microscopy(TEM). The results show that FGH98 alloy, with multi-mode size distribution γ＇phase, obtained excellent tensile properties at room temperature and intermediate temperature. The dislocations sheared γ＇phase, forming stacking fault(SF) in the γ＇precipitate and a dislocation loop around the γ＇precipitate, which is the dominant deformation mechanism during the tensile deformation at room temperature. The dislocation loop hindered the subsequent dislocation movement. However, forming SFs and deformation twins by dislocations shearing γ＇phase becomes the dominant deformation mechanisms at intermediate temperatures. With the increasing of deformation temperature, the deformation mechanisms transfer from SFs to deformation twins, and the density of twins increased. The model of a/3<112> partial shearing the γ＇precipitate forming faults and twins was given. With the increase of strain, the stacking faults accumulated on the adjacent {111} planes, promoting the formation of continuous twins. The formation of continuous twins can coordinate the deformation between the γ and γ＇phase and release the deformation stress, resulting in enhancement of the alloy plasticity.