The particle size distribution of oil⁃in⁃water emulsion prepared under different conditions was studied by Malvin laser particle size analyzer. The results showed that the particle size of the oil⁃in⁃water emulsion decreased with the increase of the concentration of the active agent. When the concentration of the active agent reached 0.5%, the emulsion system was stable and the particle size changed little with the time of standing. With the addition of polymer, the particle size of oil⁃in⁃water emulsion increased first, then decreased and then increases. Within a certain shear rate range, the particle size of oil⁃in⁃water emulsion decreased with the increase of shear rate. When the shear rate exceeded 6 000 r/min, the particle size hardly changed with the shear rate. After shearing for a certain time, the change of emulsion particle size with shearing time was very small. At low shear rate, the emulsion system formed with short shear time was unstable.