In this paper, material nonlinear behaviors of the piezoceramic, PZT5A, under high electric field and various stress conditions were experimentally investigated and the actuation performance analysis of PUMPS (piezoelectric unimorph with mechanically pre-stressed substrate) considering the material nonlinearities of the embedded PZT5A was accomplished. Empirical functions, which represent stress effects on the performance of the PZT5A, were established by measuring the induced piezoelectric strain versus electric field curves of the PZT5A under various applied stresses and electric fields. In addition, variation of the elastic modulus of the PZT5A was evaluated based on the frequency response functions under various electric fields. The nonlinear characteristics of the PZT5A were implemented in the ABAQUS simulation model for the performance analysis of PUMPS. With the nonlinear material properties of the PZT5A, the actuation displacement and force of PUMPS were accurately predicted.