Lead zirconate titanate ceramics with different contents of excess PbO, Zr/Ti ratios, and carbon nanotubes (CNTs) addition were fabricated by conventional solid-state reaction sintering in air. The effect of PbO content, Zr/Ti ratio, and the addition of CNTs on the formation of intragranular pores in Pb(Zr0.95Ti0.05)O3 ferroelectric ceramics were studied by scanning electron microscopy measurements. It was found that the formation mechanism of porous-grained ceramics is tightly associated with the stoichiometry of PbO and the addition of CNTs. The physical mechanism of the intragranular pore formation, that the insufficiency of PbO and the introduction of the CNTs decrease the densification process by inhibiting mass transportation during sintering stage, was tentatively proposed based on the sintering theory. The ferroelectric properties of the ceramics were characterized and correlated with their microstructures.