Abstract: To investigate the air flow distribution in a lit cigarette during puffing, a device for measuring the air intakes through different sections of the cigarette was designed. The air intakes from the combustion cone, cigarette paper and filter during puffing were determined with the designed device. The air flow distribution in the cigarette during puffing and the net yield of mainstream smoke generated by the combustion cone were analyzed. The results showed that: 1) The air intakes from cigarette paper and filter during puffing were higher than those of an unlit cigarette, and the air intake from the combustion cone was lower than that of the unlit cigarette, and the filter ventilation rate of a cigarette with ventilation was higher than that of the unlit cigarette. 2) During the puffing of an unventilated cigarette, the air intake from the combustion cone linearly decreased with the increase of the remaining tobacco rod length, and the air intake from cigarette paper was directly proportional to the square of the remaining tobacco rod length. 3) There was a net yield of tobacco smoke during puffing, which was directly proportional to the air intake from the combustion cone, about 0.24 mL of net smoke was produced per milliliter air intake from the combustion cone.