Piezoelectric ceramics are functional information ceramic materials that can convert mechanical and electrical energy into each other. They are widely used in high-tech fields, such as the electronics industry, machinery, and aerospace. Currently, Pb(ZrTi)O3 (PZT) piezoelectric materials are most commonly used, but the main component, PbO, is toxic and volatile during production and manufacturing, thus causing certain damage to human health and the environment. Therefore, research on green and environmentally friendly lead-free piezoelectric materials has been attracting much attention. This paper will therefore present two lead-free piezoelectric ceramics that have the potential to replace PZT-based lead-containing piezoelectric materials: Potassium Sodium Niobate (KNN)-based piezoelectric ceramics and Bismuth Sodium Titanate (BNT)-based lead-free piezoelectric ceramics. The piezoelectric constants of lead-free piezoelectric ceramics represented by systems such as KNN and BNT are now comparable to those of lead-containing piezoelectric ceramics and are gradually replacing traditional lead-based piezoelectric ceramics in fields such as ultrasonic atomization and hydroacoustic energy transfer.