Environmental barrier coatings (EBCs) with excellent chemical resistance and good high-temperature stability are of great significance for their applications in next-generation turbine engines. In this work, a new type of high-entropy fluorite-structured oxide (Ce_0.2Hf_0.2Y_0.2Pr_0.2Gd_0.2)O_2−δ (HEFO-1) with different Ti⁴⁺ contents were successfully synthesized. Minor addition of Ti⁴⁺ could be dissolved into a high-entropy lattice to maintain the structure stable, effectively reducing the phase formation temperature and promoting the shrinkage of bulk samples. Heat treatment experiments showed that all the samples remained a single phase after annealing at 1200–1600 ℃ for 6 h. In addition, high-entropy (Ce_0.2Hf_0.2Y_0.2Pr_0.2Gd_0.2Ti_0.2x)O_2−δ demonstrated great resistance to calcium–magnesium–alumina–silicate (CMAS) thermochemical corrosion. When the content of Ti was increased to x = 0.5, the average thickness of the reaction layer was about 10.5 µm after being corroded at 1300 ℃ for 10 h. This study reveals that high-entropy (Ce_0.2Hf_0.2Y_0.2Pr_0.2Gd_0.2Ti_0.2x)O_2−δ is expected to be a candidate for the next-generation EBC materials with graceful resistance to CMAS corrosion.