The polarization and depolarization of antiferroelectric Pb（Nb,Zr,Sn,Ti）O3 ceramics under dc bias were studied under hydraulic pressure ranging from zero to 250 MPa. It was found that the antiferroelectric ceramic can be induced to a metastable ferroelectric state and that the ceramic at this ferroelectric state can be switched to the antiferroelectric state by using hydraulic pressure. The hydraulic pressure that induces the transition from the ferroelectric to the antiferroelectric states increases with the positive and decreases with the negative dc bias. The electrical energy stored in the poled ceramics at its ferroelectric state releases during the transition from the ferroelectric to antiferroelectric state, which results in a strong current pulse a cross the ceramic. Based on the results, the pressure-electric field phase diagram for polarized PNZST ceramics was established.