Abstract: Abstract: Features of a truck-mounted fogger powered with a steady combustor are high efficiency, low usage, and low cost in control of forestry pest insects and diseases. The structure parameters of its exhausted tube are the key factors to affect oil solvent insecticide to atomize thermodynamically. We studied 3 types of atomizers: ring atomizer, coniform atomizer and column atomizer; 6 location points for the ring atomizer placed inner of the exhausted tube from 250 to 500 mm away from the exit of the exhausted tube; 3 structure parameters of a ring atomizer as jet flow direction of the orifices, orifice number and diameter; 3 jet flow directions as parallel to airflow, to center of pesticide ring and at 45° to airflow direction; 3 different diameters of exhausted-tubes as Φ70, Φ90, and Φ110 mm, which the experiment for atomizing effect was done respectively. The results showed that the ring atomizer was most effective in thermal atomizing; there were the defect phenomena with a coniform atomizer or a column atomizer, such as dropping liquid at the exit of the exhaust tube and combusting flame in the fog. However, the atomizing effect with the coniform atomizer was better than that of the column atomizer. The thermal fogging concentrate can atomize completely to uniform, fine droplets whose size distribution was in a narrow range of 4-6 μm, when the ring atomizer was positioned inner a Φ70 mm exhaust tube and in the range of 250-350 mm away from the exit of the exhaust tube. With the Φ90 mm or Φ110 mm exhausted tube, there were two droplet distribution regions: 4-7 μm for the fine droplet group whose volume ratio to total droplet volume was less than 16%, and 7-226 μm for the coarse droplet group,. The vast majority of coarse droplets could not be completely atomized thermodynamically. The relative span of droplet was only 0.18μm for the Φ70 mm exhaust tube, but were much higher (2.48 and 2.65μm) for the Φ90 and Φ110 mm exhaust tubes respectively. The parameters for a ring atomizer, such as the diameter, number and jet flow direction of the orifices basically did not affect the thermal atomizing performance. Thus, in the process of thermal atomizing for hot fogging concentrate, atomizer type, the exhaust tube diameter, and the position of the atomizer were the main factors influencing the performance of a thermal atomizer.