The electric polarization effect in piezoelectric ceramics of PbZrO3-PbTiO3 system (PZT) was examined by positron lifetime measurements. It was found that the mean lifetime τm increases with the increase of the electric field E. The micromechanism of the increase of τm was discussed, it may be mainly attributed to that the increase of the inner electric field would be energetically in favour of the positrons to form in qPs state. The measurements of the coupling factor K_p, the piezoelectric constant d33, and the dielectric constant ε33T/ε0 were also carried out and the results were compared with that of positron lifetime measurements. It is suggested that there is a possibility to take positrons as a tool for studying the extent of the domain turning and the changes of the energe situation of the electrons during the polarization.A special single sample method was used in the present work. Finally, our method of date analyzing was discussed.