One-dimensional piezoelectric actuators are applied in micromachining systems. To generate accurate movement in micrometer/nanometer scale, a dynamical model of the piezoelectric actuator is in need. A new approach of dynamic modeling of the actuators considering loading effect of the external structures is proposed and validated. Merging the constitutive equations of the piezoelectric materials to the dynamics of the external loading structures, dynamic model of the actuators is presented in both condition I and condition II. A general dynamic model of the piezoelectric actuator with loading structure will predict the behavior of the actuator with validation of three different excitation signals. Thanks to the linearity of constitutive equations and Fourier series of periodic signals, application of the dynamic model spreads itself to other periodic signals.