Abstract: Due to the excellent electromechanical coupling properties, perovskite inorganic nano-functional dielectrics have become a research hotspot in the field of new high voltage technologies. Compared with commercial lead-based piezoelectric ceramics, K_0.5Na_0.5NbO₃ (KNN)-based piezoelectric ceramics are environment-friendly modern electrical materials, and exhibit a high Curie temperature, low strain hysteresis and low driving polarization field. However, compared with other lead-free piezoelectric materials, the KNN-based piezoelectric ceramics have disadvantages of low electrostrain and poor temperature instability, limiting their practical application. Thereby, the principle of electromechanical coupling of piezoelectric materials is introduced firstly. Secondly, based on direct and reverse piezoelectric effects, the application status of lead-free piezoelectric substrates in electrical engineering is comprehensively summarized. Furthermore, from the viewpoint of the multi-parameter optimization and synergistic modification, the state-of-the-art and research progress in improving the electrostrain and temperature stability of KNN-based ceramics by elemental doping, compositing with second phase, heat treatment, and new preparation process are described in detail. Finally, the research priorities and the future development directions are proposed, including the development of novel piezoelectric materials with excellent electromechanical coupling performance temperature stability, the exploration of phase structure and domain structure induction mechanism of KNN-based ceramics, the research and development of multi-mechanism synergistic modification process, and the investigation on anti-aging performance of piezoelectric devices. It is expected to provide some references for designing novel piezoelectric dielectrics.