A large number of particulate size distributions of welding aerosols are measured by means of DMPS method, several distribution types are presented. Among them the single-peak distribution is the basic composing unit of particulate size. The research on the mathematic models and distributions f unctions shows that the singlepeak distribution features the lognormal distribution. The diagram-estimating method (DEM) is a concise approach to dealing with distribution types, obtaining distribution functions f or the particulate sizes of welding aerosols. It proves that the distribution function of particulate size possesses the extending property, being from quantity distribution to volume, as well as highorder moment distributions, with KS method verif ying the application of single-peak distribution and of DEM.