Two chemical compositions PbLa(Zr,Sn,Ti)O3 (PLZST) ceramics near the ferroelectric-antiferroelectric (FE/AFE) phase boundary were prepared by a traditional solid-state reaction process. The electrostriction properties under the electric field and the influence of hydrostatic pressure on the phase transition and the dielectric properties of these PLZST ceramics have been studied. Under the AC electric field, the strain of these two samples reached 0.21% and 0.13%, respectively. With increasing pressure, the FE/AFE phase transition temperature of the antiferroelectrics decreased and the antiferroelectric-paraelectric (AFE/PE) phase transition temperature increased, while the ferroelectric-paraelectric (FE/PE) phase transition temperature of the ferroelectrics decreased.