Abstract: In order to minimize tobacco particles from being drawn into the exhaust hood in the tunnel type conditioner, the exhaust hood was redesigned. As the first step, the bottom of exhaust hood was changed from open type into close type, and the height of the hood was increased by 1 m. As the second step, two air baffle plates were installed inside the hood, and a slot was created on hood wall. A mathematical model for flow field and tobacco particle movement inside the hood was established based on fluid mechanics theory, and the relationship of tobacco movement trajectory with the shape, size and inside structure of the hood was studied via numerical simulation. The results showed that: 1) After the first step, the volume of air entering into the exhaust hood reduced by 23.5%, 68.4% of the tobacco particles entering into in the hood stayed there for longer than 10 s. The airborne tobacco particles tended to build up on the hood wall, it might drop off occasionally. 2) After the second step, the tobacco that stayed in the hood longer than 10 s only accounted for 22.8%, the amount of tobacco building up on the hood wall reduced obviously. The recovery rate of tobacco particles reached 80.67%, its concentration at the exit was 37.5 mg/m³, which satisfied the requirement for allowable emission concentration, and the utilization rate of strips and cigarette quality were promoted.