Abstract: TP347H/12Cr1MoV dissimilar steel was welded with nickel-based welding wire as filler metal by TIG welding, and then the joints were subjected to different aging treatments at 650 ℃. After measuring the high temperature tensile properties of the aged joints, it was comprehensively analyzed that the microstructure of the coarse-grained zone and fusion zone on the side of 12Cr1MoV steel and the characteristics of the precipitated phases, and also the distribution of carbon concentration near the fusion line. The results show that the tensile strength and yield strength for the dissimilar steel joints gradually decrease as the aging time increases, and all the aged joints have eventually fractured on the 12Cr1MoV side after high-temperature tensile tests. The base metal of 12Cr1MoV steel before aging treatment is composed of equiaxed ferrite grains and a small amount of pearlites. With increasing the aging time, the carbides in pearlite structure gradually spheroidized and migrated to the ferrite grain boundaries in which linked in clusters or distributed in strips. The metallographic structure of the coarse-grained heat-affected zone on the 12Cr1Mo V steel side for different aged joints has no much difference,and is mainly composed of ferrite and tempered structure.The fusion line on the 12Cr1MoV steel side has gathered a large number of precipitated phases distributed in strips after welding. The size of the precipitated phases increase significantly and the strips become wider during high temperature aging treatment.