In this investigation, the electric-mechanical response of a PZT ferroelectric ceramic subjected to the combined electric-mechanical loads was experimentally observed. The effect of different compressive stress levels on the electromechanical response was examined. The stress-strain relationship was also measured. The ceramic sample was isolated from the test frame and the high voltage arcing were prevented effectively in the setup which promotes the precise measurement and makes the systemic experimental results available. With a high voltage amplifier and a servo-hydraulic test frame, the butterfly shaped strain vs. electric field curves and the electric displacement vs. electric field hysteresis loops of a soft PZT ceramic at different compressive stress levels were measured. The results show that the electric-mechanical coupled properties of the PZT ceramic are the function of the compressive stress. The switching criteria are given to account for the experimental results and to analyze the nonlinear electric-mechanical behavior relative to the domain switching process in this paper.