An ultrasonic transducer is disclosed, which includes one or a plurality of ultrasonic emitting units. Wavefronts of the ultrasonic waves emitted by the one or the plurality of ultrasonic emitting units are sphere surfaces with uniform radius, and the one or the plurality of ultrasonic emitting units can reflect ultrasound. The one ultrasonic emitting unit is configured to form a spherical resonant cavity, or the plurality of ultrasonic emitting units are configured to form a spherical resonant cavity collectively. An internal cavity of the spherical resonant cavity has a spherical shell shape or a cross-sectional spherical shell shape with a spherical center therein. The ultrasonic waves emitted by the one or the plurality of ultrasonic emitting units are focused on an area in which the spherical center of the spherical resonant cavity is located. The ultrasonic transducer not only can be provided with a large ultrasonic emitting area and a great focusing gain that render the energy of the ultrasonic focus enhanced dramatically, but also can be free from the influence of work frequency of an ultrasonic source.