Abstract: The high temperature tensile deformation behavior and fracture mode of a new Fe-Ni based wrought superalloy HT650P for main steam pipe at 650 ℃ advanced ultra-supercritical (A-USC) unit were studied in the range of 600 ℃ to 750 ℃. The initial microstructure of the alloy after solid solution treatment and aging treatment as well as the microstructure after high temperature tensile deformation were characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques. The results show that compared with the aged alloy, the solid solution alloy exhibits dynamic strain aging (DSA) during high temperature tensile deformation, and it gradually weakens with the increase of the deformation temperature. The γʹ phase precipitated during the aging process makes the ultimate tensile strength and yield strength significantly higher than those of the solid solution alloy. With increasing the deformation temperature, the fracture mode of the solid solution alloy changes from transgranular fracture to a mixed fracture mode in which transgranular fracture and intergranular fracture coexist, while the aged alloy has always been a mixed fracture mode. Cracks are preferentially initiated and propagated at the grain boundaries, slip bands and large MX phases. In addition, with increasing the deformation temperature, the preferred orientation of grains after tensile deformation change from <111>//RD to <001>// RD as a whole.