Abstract: Titanate are one of the important candidates for solidifying high-level radioactive nuclear waste (HLW) and lanthanide (Plutonium) due to its excellent physical and chemical durability. Polycrystalline Lu₂Ti₂O₇ and Lu₂TiO₅ ceramic materials were prepared by a conventional ceramic sintering process, then the samples were irradiated with 800 keV Kr²⁺ at room temperature, and were subsequently characterized by GIXRD method. In the two kinds of samples, lattice swelling was observed firstly, and then amorphization phase transition took place. However, the lattice swelling of Lu₂Ti₂O₇ is greater than that of Lu₂TiO₅. In addition, when Lu₂Ti₂O₇ and Lu₂TiO₅ were irradiated to a fluence of 2×10₁₄ ions/cm₂, the amorphous content of Lu₂TiO₅ sample reaches 95.54%, while the amorphous content of Lu₂Ti₂O₇ sample is only 74.66%. The first-principle was used to calculate the lattice swelling of Lu₂Ti₂O₇ with increasing of anti-sites concentration. The results show that the lattice swelling of Lu₂Ti₂O₇ before amorphization is mainly caused by the cation anti-sites. While the pristine Lu₂TiO₅ is a disordered fluorite structure, so that no cation anti-sites will contribute to the lattice swelling of Lu₂TiO during the ion irradiation process. Therefore, the lattice swelling of Lu₂TiO₅ is lower compared to that of Lu₂Ti₂O₇.