Abstract: To achieve online puff-by-puff analysis on particulate matter in mainstream cigarette smoke, a split-flow injection method that could adjust the smoke sampling volume was developed to minimize smoke cross-contamination between different puffs. Furthermore, an online detection device was established to detect the puff-by-puff release of mainstream cigarette smoke by combining the split-flow method with the extractive electrospray ionization mass spectrometry (EESI-MS). The experimental parameters were optimized and the stability of the device was evaluated. The trends of puff-by-puff release of different mainstream smoke components were analyzed, and some of these components were compared across cigarettes of different circumferences. The results showed that: 1) Under the optimized experimental parameters for targeted analytes, sharp peaks and stable baseline in total ion chromatograms (TIC) were achieved, and the device exhibited good stability with RSD less than 3%. 2) Within 100-600 mass to charge ratio (m/z) range, abundant peaks were observed in the mainstream smoke, and the puff-by-puff releases of components corresponding to different m/z mainly showed in three types as follow: first increase and then decrease, first increase and then tending to be stable, or first increase and then continuous increase. 3) For those components corresponding to the same m/z, the puff-by-puff release profiles of the slim cigarette were similar to those of the conventional king-sized cigarette, but the puff-by-puff release of slim cigarettes were more stable.