To research the influence of spray operation parameters on droplet size distribution of flat fan nozzle, experiments were conducted by using an open circuit wind tunnel and a Sympatec laser diffraction analyzer. The droplet size of reference nozzle was tested to classify the nozzles’ spray spectra. The droplet size distribution generated by different types of nozzles at different spraying pressure for different wind speed with various distances between the nozzle and the laser beam was analyzed. Experimental results showed that the VMD and percentage of the total volume contained in droplet sizes less than 150μm increased with the increasing of the spray pressure, wind speed and distances between the nozzle and the laser beam. Moreover, the classifications of nozzle’s spray spectrum became lower when the pressure and wind speed rose. The distance between the nozzle and the laser beam and wind tunnel experiment could be used to ensure the accuracy and reliability of measurement results when the laser diffraction analyzer was used to test the droplet size.