Abstract: The piezoelectric transformer is a device that transforms voltage by piezoelectric effect and converse piezoelectric of ceramic material. Compared with electromagnetic transformer, it has favorable characteristics of miniaturization, electromagnetic-noise free and the variable voltage gain with fre-quency and impedance. In this paper, the ferroelectric domain structure, properties and the effect of doping of ferroelectric-ceramic material are reviewed, and the principle of transforming voltage, the equivalent circuit and variable piezoelectric transformer are also shown. And furthermore, the problem of piezoelectric transformer is analyzed and the prospects of piezoelectric transformer is forecasted.