Five titanium-centered heteropoly acids with different metal vacancies were prepared first, and then combined with an ionic liquid by ion exchange to prepare heteropoly acid ionic liquid catalysts Bmim_4–6[M(H₂O)TiMo₁₁O₃₉] (M = Cu²⁺, Fe²⁺, Pb²⁺, Ti⁴⁺, and Zn²⁺). The structure and thermal properties of each catalyst were tested and analyzed by Fourier transform infrared (FTIR) spectroscopy, ultraviolet (UV) spectroscopy, X-ray powder diffraction (XRD), apparent morphology analysis, and thermogravimetric analysis (TGA). Five heteropoly acid ionic liquids were investigated by using waste mineral water bottles as samples for performance in the catalytic degradation of bottle-grade polyethylene terephthalate (PET), and the degradation product, bis(2-hydroxyethyl) terephthalate (BHET), was analyzed for the chemical structure. The results showed that the five heteropoly acid ionic liquid catalysts were successfully prepared, with good thermal stability. Of these catalysts, Bmim₄[Ti(H₂O)TiMo₁₁O₃₉] showed the optimal catalytic performance. It achieved an alcoholysis rate of 100% and a yield of BHET of 84.73% with a catalyst dosage of 0.6% (percentage in the total mass of the raw materials) at 190 °C for 5 h. Moreover, after six cycles of use, the alcoholysis rate was still as high as 94.36%, and the yield of BHET was 75.65%. The above results indicated that the prepared heteropoly acid ionic liquid catalysts showed good performance in the catalytic degradation of bottle-grade PET, presenting a promising prospect for development.