Using large-sized and mono-dispersed seeded latex as medium plus a semi-continuous monomer-feeding technology was an effective method for preparing high-solid content (HSC) latex. A series of runs indicated that the influence of key factors, such as surfactant, monomer composition, seed particle size, reaction temperature, and feeding rate were the most sensitive issues in maintaining the stability during preparation of HSC Poly (methyl methacrylate/n-butyl acrylate/acrylic acid) [P(MMA/BA/AA)] latex. It was also shown that the effect of these factors on the coagulum content played an important role in preparation process. In addition, the amount of gel content was more related to re-nucleation and particle size distribution (PSD) control. And the results seemed to be more different from that of produced in a low disperse phase system by conventional semi-continuous emulsion polymerization.