The antiferroelectric ceramics are often subjected to mechanical loading in transducer and high-strain actuator applications. How the electromechanical behavior changes under different load conditions is therefore very crucial for design. The electromechanical behavior of La-modified antiferroelectric ceramic lead zirconate titanate stannate (PLZST) under uniaxial compressive prestress is observed at stress up to 100 MPa using a homebuilt experimental setup in conjunction with a modified Sawyer-Tower circuit. The PLZST ceramic researched in this paper is near the ferroelectric-antiferroelectric phase boundary, and it has a lower forward phase transition electric field and slimmer electric hysteresis loop than conventional antiferroelectric ceramics. The results reveal that the area of the double hysteresis (P-E) loops, the saturation polarization (P(sat)), the longitudinal strain (S), and the remanent polarization (P(r)) decrease with increasing compressive prestress, while the forward phase transition field increases as the compressive prestress increases. Meanwhile the applied prestress virtually does not affect the transition field hysteresis (DE) and the coercive field (E(c)). These results are interpreted through the non-180 degrees domain switching processes and the stress induced decrease in the switchable part of ferroelectric and antiferroelectric domains under electric field.