Abstract: In order to study the relationship between the structure of cigarette burning cone formed during burning and the CO release in mainstream cigarette smoke, an embedding and slicing method was applied to analyze the inner structure of burning cone. The mechanism of burning cone surface porosity and its influence on CO release was analyzed in order to reduce the CO release by adjusting the burning cone structure. The main conclusions were: 1) The cone surface porosity significantly negatively correlated to the CO release. Larger surface porosity resulted in looser structure of the burning cone and more fully combusted cut tobacco, and thus the CO release in mainstream cigarette smoke became lower. 2) Via reducing the filling density of cut tobacco and adding expanded cut tobacco at a low proportion, the surface porosity was enlarged and the CO release decreased. 3) Comparing with the control cigarette sample, the surface porosity of the burning cone could be increased from 18.25% to 35.60% and the CO release reduced by 12.30% when 1% expandable graphite was added to the cut tobacco. Furthermore, the hazard index of the cigarette decreased from 7.31 to 7.01.