In this article, PBA/P(MMA-crosslinking agent)-composite particle latexes were prepared by semicontinuous seeded emulsion polymerization. To determine the seed emulsion＇s saturating capacity of an emulsifier, a mathematical model was built to simulate the changes of the seed PEA emulsion＇s surface tension with the amount of emulsifier added dropwise. The effects of the emulsifier amount added in the second stage and the addition method on the morphology of the composite particles were studied. The results were shown as follows : If the amount of emulsifier added in one batch to the seed emulsion in the second stage was less than or equal to the saturating capacity of emulsifier of the seed emulsion (Cs), the morphology of the particles was "core-shell"; otherwise, a few particles were of a core-shell structure. However, if shell materials were preemulsified and added dropwise at an appropriate rate, the latex particles were still of a core-shell structure, even when the amount of emulsifier added to the seed emulsion was greater than the Cs.