Abstract: In order to study the puff-by-puff releases of key smoke components of an electrically heated cigarette (IQOS), a mathematical model of the heat and mass transfer processes and the key smoke components in tobacco section was established to study a chemical reaction controlled and a mass transfer controlled mechanism, respectively. The results showed that: 1) The volume averaged temperature in the tobacco section under heating was mainly affected by the temperature curve of the heater and environmental heat dissipation. 2) Upon reaching the heating temperature, the puff-by-puff releases of glycerol, nicotine and propylene glycol were mainly controlled by a chemical release mechanism, and their activation energies were 33.3, 11.9 and 5.6 kJ/mol, respectively. 3) The puff-by-puff releases of water and the other components were mainly controlled by external convection caused mass transfer with the mass transferring coefficients of 0.002 and 0.009 s^-1 respectively. The mathematical model could reasonably simulate the release of the key components from the tobacco material, such as the puff-by-puff residual quantity, puff-by-puff released quantity and mass fraction.