3-1 type and 3-3 type porous PZT ceramics were fabricated by the alginate ionotropic gelation process and gelcasting technology respectively. The resultant samples were sintered at different temperatures and characterized in terms of both microstructure and piezoelectric properties. It was noted that the porosity and grain size of porous PZT ceramics increased with the sintering temperature increasing from 1 150 to 1 250 ℃, which resulted in the increase of relative permittivity, piezoelectric efficient, thickness coupling coefficient kt and compressive strength, the corresponding decrease of hydrostatic voltage coefficient and hydrostatic figure of merit (HFOM). Under the joint effects of unidirectionally aligned channels and the incorporation of Ca2+ into PZT matrix, the 3-1 type PZT ceramics possessed higher εr and compressive strength, lower d33 and HFOM than that of 3-3 type PZT ceramics. However, the maximum HFOM value of 3-1 type PZT ceramics achieved 4 755×10-15 Pa-1, which makes it suitable for the application of underwater sonar detectors.