Particle diameter distribution on insulator surface has important influence on the surface leakage current and pollution flashover voltage. This paper found that particle diameter distribution on porcelain insulator surface used on high voltage transmission lines has significant statistical characteristics. In order to find out the reason of these statistic characteristics, the adhesion process of particle was simulated based on computational fluid dynamics and collision model, and the influences of different factors were studied. The results show that under the typical meteorological conditions, particle diameter distribution on the porcelain insulator surface has statistic characteristics, which is mainly distributed in $5\mu \mathrm {m}-50\mu \mathrm {m}$. In addition, relative humidity and wind speed have a significant effect on particle diameter distribution. The effects of aerodynamic type, electric field type and electric field strength are relatively weak. This work can provide powerful support for further research work on contamination simulation experiment and influence of particle diameter on pollution flashover.