The homopolar charge and heteropolar charge appeared in polarized ferroelectric ceramics result in pyroelectric relaxation effect. Three types of relaxation process given by the phenomenological theory are observed. Since energy is needed for the excitation of homopolar or heteropolar charge, at times long after the temperature change of the ceramic, the pyroelectric charges decay slowly as △Q(t)=(1+r±e(-(α±t)1/2)△Q∞.The theory is in good agreement with all experimental data for dozens of kinds of ceramic which have been measured.