In this paper, taking the d33-mode piezoelectric transducer represented by PZT-5H as the research object, the relationship between the actual open circuit voltage of piezoelectric ceramics and the loading frequency is deduced and the necessity of considering the influence of dielectric loss is analyzed. By designing a verification test and using a finite element simulation method, the agreement between the predicted values and the tested values are verified under different transducer structures (single-plate and multi-plate stacking), different loading amplitudes, and different loading frequencies. Based on the experimental results of different structures of piezoelectric transducers, loading amplitudes and frequencies, the correctness of the formula was verified. The experimental results show that the actual open circuit voltage of the piezoelectric ceramics keeps non-linearly increasing with the increase of loading frequency at relatively low loading frequency, while increases slightly when the loading frequency gets higher. The predicted value of the theoretical formula is in good agreement with the test value. The theoretical formula deduced in this paper can be used for the prediction and analysis of the actual output voltage of PZTs.