The SEM, EBSD and TEM were used for analyze the microstructure morphology and distribution characteristics of inertial friction welded joint in welding state and post-welding heat treatment state. In addition, the mechanical properties of the joint in post-welding heat treatment state were studied. The results showed that the weld zone was single equiaxed α grains, which is composed of lamellar martensite α" phase + grain boundary lamellar αP phase + metastable β phase in welding state, and with (0001)//ND fiber texture. The microstructure was consisted of grain boundary lamellar αP phase + intragranular lamellar αS +β phase after post-weld heat treatment. The (21 ?1 ?3)[21 ?1 ?9] orientation texture was also formed on the basis of the original fiber texture. Under the effect of welding pressure and thermal cycling, the equiaxed αP phase in thermo-mechanically affected zone had been transformed into a rod and approximately paralleled to the welding interface. The equiaxed αP phase in thermal affected zone still maintained original shape. The weld zone had the highest microhardness, which gradually decreased from weld zone to base metal. The post-weld heat treatment can reduce the hardness of the weld zone and obtain uniform hardness distribution in welded joint. The tensile specimens at room temperature failed in the base metal away from weld center line.