Abstract: Accurately measuring and controlling the droplet size is important for icing wind tunnel tests. To study droplet characteristics and its effects in the 3m×2m icing wind tunnel, a PDI-FP (Phase Doppler Interferometer Flight Probe)system is used for the MVD (Median Volume Diameter) measurement and control test, and the effect factors such as pressure, airspeed, and temperature are analyzed. The experimental results show that there are sensitive relationships between the droplet size and spray air/water pressures. The MVD is inversely proportional to the spray air pressure. The air speed and temperature don't have impact on MVD obviously with the maximum deviation less than ±10%. The MVD is significantly reduced by applying negative pressure.