To adjust the size and size distribution of miniemulsified butyl acrylate（BA）droplets containing nanometer silica particles，the influences of the composite of miniemulsification system and the ultrasonic conditions on the size and size distribution of droplets were investigated.It was found that there existed critical ultrasonic power and time for achieving a stable size and size distribution of droplets.The droplets size decreased as the concentration of sodium dodecyl sulfate（SDS）increased，while the concentration of hexadecane had no significant influence on the droplet size.The droplet size increased and the droplets size distribution widened as the mass fraction of silica in BA dispersion，and the BA dispersion/water mass ratio increased.It was confirmed that the existence of nanometer silica particles in BA had a certain influence on the miniemulsification of butyl acrylate as the nanometer silica particles consumed a part of the ultrasonic power and changed the physical characteristics of the disperse phase.When the storage and polymerization temperatures were below 65℃，stable miniemulsion and corresponding poly（butyl acrylate）/nanosilica composite latex could be obtained.