Abstract: In order to investigate the particle size distribution of atomized casing solution and optimize tobacco casing in cigarette production, two high-speed cameras, an external-mixing air atomizing nozzle testing platform, and Halcon image processing software were used to analyze the influences of the flow rate and temperature of casing and the air pressure in nozzle on the particle size distribution of atomized casing. At the same time, the uniformity distribution function of atomized droplets' diameters and the experimental mathematical model of Sauter mean diameter were established by discrete uniform distribution method and dimensional analysis method respectively. The results showed that keeping the other conditions unchanged, 1) the distribution uniformity of droplets promoted gradually as the testing area varied, and the biggest variation of distribution uniformity presented in area No.4 statistically; 2) the distribution uniformity of droplets decreased gradually with the increase of air pressure in nozzle; 3) the distribution uniformity of droplets increased gradually with the rise of casing flow rate, however, it decreased first and then increased with the rise of casing temperature; 4) SMD value changed irregularly with the rise of casing temperature and air pressure, however, it reduced first and then rose with the increase of casing flow rate and air pressure, lowered gradually with the rise of temperature and flow rate of casing.