It is well known that there is a pinning effect of oxygen vacancies. The migration rate of an oxygen vacancy in crystalline ceramics is lower than the rate of spontaneous polarization, which limits the improvement of piezoelectric properties. In this work, Pr and Ce elements were introduced into position A of Na_0.5Bi_4.5Ti₄O₁₅ to improve the piezoelectric properties of Na_0.5Bi_4.2-xCe_xPr_0.3Ti₄O_y ceramics. The Ce-doping effectively modulated the content of oxygen vacancies by different doping amounts so that the difficulty of domain inversion caused by oxygen vacancy motion was reduced and insufficient polarization was improved. As a result, the best piezoelectric properties (d₃₃ = 22 pC/N) and low dielectric loss (tan δ = 0.003) were achieved at 10 KHz under 200°C with a substitution of 0.025 mol in Na_0.5Bi_4.2-xCe_xPr_0.3Ti₄O_y ceramics. The high dielectric constants and low dielectric loss greatly improve the energy conversion efficiency, so this ceramic has great prospects in the application of medium- and high-frequency ultrasonic transducers.