Abstract: Nozzle is widely applied in the devices of wet desulphurization，dust removal and others ，the D₅₀ of the atomized droplets is the key parameter to evaluate the nozzle. Atomization experiments of different pressure and distance for the nozzle with the apertures of 1 . 44 μm and 0 . 46 μm were carried on ，and the uncertainty values of the D₅₀ of the atomized droplets are calculated with uncertainty evaluation method. The experiment and evaluation results indicate，the D₅₀ value of the atomized droplets changes a lot with the change of atomized conditions ，but the deviation of the D₅₀ values inthe same conditions is small with the maximum value of measure of uncertainty being 5 μ m.And the further conclusion is that the D₅₀ of the atomized droplets is determined by the structure of nozzle，and it is reliable to guide these lection of nozzle with D₅₀.

Key words: D ₅₀, atomizeddroplet, uncertaintymeasurement, sprayingnozzle