With the development of science and technology and environment, lead-free piezoelectric ceramics has been a necessary trend, and potassium-sodium niobium (KNN) based lead-free piezoelectric ceramics has become a hotspot because of its high Curie temperature and piezoelectric properties. This paper firstly summarizes and analyzes the study direction and actuality of potassium-sodium niobium (KNN) based lead-free piezoelectric ceramics from new component, ions substitute, sintering reagent and temperature dependence in recent years, and then indicates the future hotspot and problem. We think it can improve the temperature stability to introduce diffusion mechanism into KNN based ceramics. Meanwhile, we also should study the effect of nano-sized domain on properties of KNN ceramics. At last, the paper forecasts the future study direction——the study of electric properties, of temperature stability and micro mechanism.