Dynamic hysteresis of Nb-doped Pb(Zr1-xTix)O-3 (PZT, 0.20 <= x <= 0.60) ceramics were studied systemically at different field (E) and frequency (f). The hysteresis loops were strongly dependent on E and f. The measured coercive fields (E-c0) were far lower than the calculated values based on the Landau-Ginzburg theory, and increased dramatically from the rhombohedral phase to the tetragonal phase while had less variation with composition in the same phase. With increasing E or f for each composition, three types of loops were observed: linear, minor, and saturated loops. The cross fields (E-0), cross polarizations (P-0), and hysteresis areas (< A >) showed different variation regularities with f. Similar varying curves were observed for all PZT ceramic samples by normalizing E-0, P-0, and < A > with E/E-c0, which indicated the same polarization switching for different domain structures. Further analyses revealed that the switching processes can be divided into three stages: space charge polarization, domain switching, and steady state. The first and second stage occurred at similar to 0.5 and similar to 1.5 E/E-c0, respectively. These results would be very helpful to further understand the polarization switching of ferroelectric ceramics.