Abstract: The load frequency characteristics of high-voltage and low-current power supply converter based on piezoelectric transformer (PT) is researched in this paper. The equivalent lumped-parameter circuit model of PT was used to analyze the load frequency characteristics of PT, it showed that the operating frequency of PT was getting high as the increase of load resistance, and eventually reached a saturation value. The experiment was carried out using KHMPT3206 PT as the subject. The result found that the experimental measured frequency was consistent with theoretical calculation frequency when the load was less than 50 kΩ, while the load was greater than 50 kΩ, the maximum relative error would be 2.5%. The correctness of equivalent lumped-parameter circuit model is verified. The cause that the operating frequency is influenced by load can be explained as that the change of load affects the equivalent series capacitance and further leads to the change in operating frequency of PT.