As an environmentally friendly piezoelectric material, the (K,Na)NbO3-based (KNN) lead-free piezoelectric ceramics with a high Curie temperature and a tunable phase boundary structure show potential application prospects in the piezoelectric devices and have attracted extensive attention lots of research interesting. In this work, the research progress of KNN-based materials was reviewed from the aspects of phase composition, preparation process and performance control. Especially, its practical application in the field of piezoelectric devices was systematically introduced. Finally, the future research and development direction of KNN and its application in device were summarized and prospected.