Abstract: To synergistically optimize the piezoelectric and strain properties along with the Curie temperature, 0.30PNN-xPYN-(0.31−x)PZ-0.39PT quaternary piezoelectric ceramics were fabricated via a conventional solid-state reaction process at sintering temperatures ranging from 1140 to 1200 °C. The effects of PYN content on the microstructure and electrical properties were systematically investigated. Results indicate that a slight increase in PYN leads to an enlargement of ceramic grain size. The density of the ceramic exhibits a non-monotonic trend, first increasing and then decreasing as the PYN proportion rises. Correspondingly, the dielectric, piezoelectric, and ferroelectric properties all demonstrate a similar trend of initial enhancement followed by degradation with increasing x. Analysis of the temperature-dependent dielectric loss suggests that PYN incorporation effectively reduces the leakage current and improves the high-temperature stability of the ceramics. The samples with x = 0.05 exhibit the best piezoelectric properties due to their most uniform and compact microstructure and optimal PYN content. The optimal overall performance was achieved in the 0.30PNN-0.05PYN-0.26PZ-0.39PT sample (x = 0.05) sintered at 1160 °C, exhibiting excellent properties of P_r ≈ 39.07 μC·cm⁻², k_p = 0.68, tanδ = 1.6%, d₃₃ ≈ 715 pC·N⁻¹, and S ≈ 0.144% @ 20 kV·cm⁻¹. This work clarifies the regulatory mechanism of PYN content on the performance of PNN-PYN-PZT ceramics, providing an important basis for designing high-performance piezoelectric driving materials with high Curie temperatures.