This paper presented a novel modified Q-states Potts Monte-Carlo computer simulation procedure applied to simulate the grain growth of intermediate and final stages of sintering and Ostwald ripening process of BaTiO3 Positive Temperature Coefficient of Resistance (PTCR) ceramics, and the effects of liquid-phases on the grain growth of BaTiO3-based PTCR ceramics. The computer simulating models of the grain growth of the sintering process were established by the theory of the grain growth. The simulating results indicated that (1) the liquid-phase would hinder the motion of the grain-boundary, and the ratio of the grain growth was limited so that the size of the grains was smaller than those of the single-phase system; (2) the shrinkage of a BaTiO3 PTCR ceramics almost ceased at the temperature of 1513 K or so in the two-phase system, and the soaking stage involved the densification and grain growth of ceramics controlled by liquid-phases.