Abstract: Domestic T91 and 316Ti steels were irradiated by 200 keV Xe⁺ ions at room temperature. The phase stability and microstructure evolution under different irradiation damage doses were investigated with X-ray diffraction (XRD) analysis and transmission electron microscope (TEM). The results show that there is no obvious new phase after irradiation in T91 steel. The martensitic phase transformations from γ (FCC) to α (BCC) are observed in 316Ti steels, and the α phase content increases with the irradiation damage dose. The main contribution to the driving force for the martensitic phase transformations is the plastic deformations induced by the formation of Xe precipitate. M₂₃C₆ particles in T91 steel appear amorphous, and become evident with the increase of the irradiation damage dose. The amorphization is attributed to the fact that the Xe⁺ ions weaken the lattice of M₂₃C₆ locally, and the lattice collapses to amorphous state. Black spots are found in 316Ti steels which are irradiated at low doses (below 4.6 dpa), and dislocation loops form from black spots aggregation at high dose (37.1 dpa).