Nb-doped lead zirconate stannate titanate ferroelectric ceramic with composition Pb0.99Nb0.02[(Zr0.90Sn0.10)0.96Ti0.04]0.98O3 (PZST 90/10-4-2Nb) is studied in a hydraulic pressure range of 0300 MPa by released charge and dielectric measurements. Pressure-induced low temperature phase transition from ferroelectric rhombohedral (FR(LT)) structure to antiferroelectric orthorhombic (AO) strueture is investigated. Unpoled, poled and pressure-depolarized PZST 90/10-4-2Nb ferroelectric ceramics are used. The released charge quantity is 29.3 C/cm2 and the threshold pressure is 140 MPa during the phase transformation from FR(LT) structure to AO strueture. Dielectric properties show that the threshold pressure of the phase transformation from FR(LT) structure to AO structure is 136 MPa for poled ceramic and 104 MPa for unpoled ceramic. Obvious characteristic of phase transformation is not observed in pressure-depolarized ceramic.